A requirement version can be marked as final by the owner once all reviewers have accepted the version. The owner can choose to mark a version as final directly without having any reviewers added to the requirement version. This is called self approval.
To mark a version as final in the Versions tab of the requirement, the requirement owner can click the Draft button and choose Mark Final.
Users will need to be the requirement owner, and have project permissions to view and edit the requirement to perform this action.