According to the PMBOK Guide, a scope change request is a formal proposal to modify any project document, deliverable, or baseline. It is an output of the Perform Integrated Change Control process, which is the process of reviewing all change requests, approving changes, and managing changes to the deliverables, organizational process assets, project documents, and the project management plan. A scope change request may introduce new risks or affect existing risks on the project, which may impact the project objectives, such as scope, schedule, cost, and quality.
The risk manager should support the project manager with the scope change request by evaluating any new risks that are introduced due to the change in scope. This is because the risk manager is responsible for planning, implementing, and monitoring the risk management activities on the project, as well as communicating and reporting the risk information to the project manager and other stakeholders. The risk manager should use the appropriate risk identification and analysis techniques, such as brainstorming, interviews, checklists, SWOT analysis, cause and effect diagrams, probability and impact assessment, etc., to identify and evaluate the new risks that may arise from the scope change. The risk manager should also document the new risks in the risk register, which is a project document that contains the details of all identified individual project risks and other relevant information.
The other options are not valid for what the risk manager should do to support the project manager with the scope change request:
Update the risk management plan to reflect the scope change: This is not a valid option because the risk management plan is a component of the project management plan, which describes how risk management activities will be structured and performed on the project. It is an output of the Plan Risk Management process, which is the process of defining how to conduct risk management activities for a project. The risk management plan should not be updated to reflect the scope change, but rather to reflect any changes in the risk management approach, methodology, roles and responsibilities, budget, timing, risk categories, definitions, reporting formats, etc. The risk management plan should be updated only when there is a change in the risk management process, not in the project scope.
Reassess the identified risks that impact the project scope: This is not a valid option because reassessing the identified risks that impact the project scope is part of the Monitor Risks process, which is the process of implementing risk response plans, tracking identified risks, monitoring residual risks, identifying new risks, and evaluating risk process effectiveness throughout the project. The risk manager should not reassess the identified risks that impact the project scope before evaluating any new risks that are introduced due to the change in scope. The risk manager should first identify and analyze the new risks, and then reassess the existing risks to determine if they are still valid, relevant, and prioritized.
Update the risk register to identify, analyze, and plan a response for any new risk: This is not a valid option because updating the risk register to identify, analyze, and plan a response for any new risk is a combination of several risk management processes, such as Identify Risks, Perform Qualitative Risk Analysis, Perform Quantitative Risk Analysis, and Plan Risk Responses. The risk manager should not update the risk register to identify, analyze, and plan a response for any new risk in one step, but rather follow the sequential and iterative risk management processes to ensure a comprehensive and consistent risk management approach.
The risk manager should also coordinate and communicate with the project manager and other stakeholders when updating the risk register, as well as obtain their approval and input.
PMBOK Guide1, Risk Management Professional (PMI-RMP) Cert Guide1

Risk impact assessment involves calculating the impact of identified risks. Risk analysis is the process of examining, estimating, and evaluating the impact of risks, which helps in calculating the impact (Reference:
PMBOK Guide, 6th Edition, p. 417)
Risk analysis is the process of assessing the likelihood and impact of the identified risks on the program objectives. It helps to calculate the impact of the risks by using qualitative or quantitative methods. Risk analysis can provide useful information for risk prioritization, risk response planning, and risk reporting. References: PMI, The Standard for Risk Management in Portfolios, Programs, and Projects, 2019, p. 67; PMI, The Standard for Program Management, Fourth Edition, 2017, p. 113.