If the objective is just to make an update from an old user to the current user, you can simply update the 'Assigned to' field and may be add some comments about why it was updated.
But the general scenario should be addressed as part of the overall HAM process. An example is given below:
When a user returns an asset, it should go back to the stockroom first. If the asset is nearing end of life, it should be marked as retired and ready for disposal. Then the disposal process will follow. If the user has returned for another reason (E.g. user leaving the company - part of offboarding process) and the asset is still in good condition, it will again go back to the stockroom first. But now it can be deployed to another user from a location serviced by that stockroom who places a request for the same model. The assignment of the asset to the user should happen automatically once the request is completed.
