I have a user with an Arcgis pro license, who borrowed the license to work offline. This laptop where the license was in offline mode had damage to the hard drive, so it was required to replace it. The fact is that the license is assigned to the computer and does not allow me to deauthorize it, remove it, or delete the user. As is done in this case to be able to release or recover the license.
Here is an article describing what I think you need to do. I am not myself familiar with the process.
How To: Recover lost licenses from My Esri