Explanation
According to the Official CompTIA A+ Core 1 Study Guide (220-1101) 1, the correct answer is A. Document the findings, actions, and solution in the company knowledge base.
The explanation is that after resolving an issue, a technician should always document what was done and how it was fixed. This helps to create a record of the problem and its solution for future reference and also to share knowledge with other technicians.
https://www.comptia.org/training/books/a-core-1-220-1101-study-guide
By documenting the findings, actions, and solution in the company knowledge base, it will help to ensure that if the Issue happens again, the technician or a different technician will be able to quickly and easily find the solution and resolve the Issue. Additionally, it is important to document the solution so that the same Issue does not need to be troubleshot multiple times in the future.

When experiencing issues accessing a USB key for a firmware update, particularly in relation to system board UEFI updates, the Secure Boot feature should be considered. Secure Boot is a security standard designed to ensure that a computer boots using only software that is trusted by the PC manufacturer. If Secure Boot is enabled, it might prevent the system from recognizing or booting from the USB key if the firmware update or the USB drive is not recognized as a trusted source. Disabling Secure Boot temporarily can allow the firmware update to proceed.

After the issue has been identified and the backup of the system has been made, the next step is to establish a theory of probable cause. This involves researching the issue to determine the root cause of the problem. This can involve researching internally (e.g. referring to the system logs) or externally (e.g. searching online).
Once the probable cause has been identified, the technician can then move on to the next step of designing a plan of action to resolve the issue and implementing the solution.