According to the PMI Risk Management Professional (PMI-RMP) Reference Materials, the project management plan is the document that describes how the project will be executed, monitored, and controlled. It integrates and consolidates all the subsidiary plans and baselines from the project management processes1. The project management plan should be updated whenever there are changes in the project scope, schedule, cost, quality, resources, communications, risks, procurements, or stakeholder engagement2. In this case, the project team has decided to log the opportunities in the current project's risk register, which is a component of the project management plan. Opportunities are positive risks that may have a beneficial effect on the project objectives, such as cost savings, schedule acceleration, or quality improvement3. Therefore, the project team should update the project management plan to ensure the results of the opportunities are captured and reflected in the relevant subsidiary plans and baselines. For example, if an opportunity leads to a cost saving, the project team should update the cost management plan and the cost baseline accordingly.
References: 1: PMI, A Guide to the Project Management Body of Knowledge (PMBOK Guide), Sixth Edition, 2017, p. 89 2: PMI, A Guide to the Project Management Body of Knowledge (PMBOK Guide), Sixth Edition, 2017, p. 123 3: PMI, A Guide to the Project Management Body of Knowledge (PMBOK Guide), Sixth Edition, 2017, p. 397

The project manager should implement the risk handling strategies for the risks that occur more frequently, as this will help reduce their impact on the project and improve overall project performance.
Exploit is a positive risk response strategy that aims to ensure that the opportunity is realized 1. It involves eliminating the uncertainty associated with a particular upside risk and making it happen 2. For example, if there is an opportunity to reduce the project cost by using a cheaper supplier, the project manager can exploit it by signing a contract with the supplier and securing the savings. Exploit is the opposite of avoid, which is a negative risk response strategy that seeks to eliminate the threat or protect the project from its impact 2.
The other options are not appropriate for taking full advantage of opportunities. Mitigate is a negative risk response strategy that reduces the probability and/or impact of a threat 2. It is the opposite of enhance, which is a positive risk response strategy that increases the probability and/or impact of an opportunity 1. Accept is a risk response strategy that involves acknowledging the risk and not taking any action unless the risk occurs 2. It can be applied to both threats and opportunities, but it does not actively pursue them. Transfer is a negative risk response strategy that shifts the impact of a threat to a third party, along with ownership of the response 2. It is the opposite of share, which is a positive risk response strategy that allocates ownership of an opportunity to a third party who is best able to capture it for the benefit of the project 1.

Risk identification should be an ongoing process throughout the project lifecycle. Encouraging project team members to proactively identify risks allows for continuous risk management and the development of appropriate response strategies as new risks emerge.
According to the PMI Risk Management Professional (PMI-RMP) Examination Content Outline1, one of the tasks in the domain of Risk Identification is to ensure that project team members proactively identify risks throughout the project life cycle, using various tools and techniques, to enable planning for possible risk response strategies1. Risk identification is an iterative process that should be performed regularly and frequently throughout the project, as new risks may emerge or existing risks may change due to internal or external factors2. The project manager should involve the project team members and other relevant stakeholders in the risk identification process, as they may have different perspectives, expertise, and insights on the project risks3. The project manager should not identify risks only at the project's midpoint for the stakeholders to review them, because that would be too late and ineffective to manage the risks that may have already occurred or escalated4. The project manager should not identify risks at the beginning of the project because the risk posture will not change, because that would be unrealistic and imprudent to assume that the project environment and conditions will remain static and predictable5. The project manager should not delegate risk identification to each team member and have them record the risks on separate risk registers for their areas, because that would create inconsistency, duplication, and fragmentation of the risk information, and prevent a holistic and integrated view of the project risks. References: 1: PMI Risk Management Professional (PMI-RMP) Examination Content Outline, page 82: A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Sixth Edition, page 3983: A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Sixth Edition, page 3994: Risk Identification: When and How Often to Do It During the Project Life Cycle5: Risk Management: Why Is It Important?. : Risk Register in Project Management - Project Management Academy.