The team administrator of your organization has the ability to add an owner to any proof that is owned by a user in the team.
Team administrators: Adding an owner
In the main menu, select teams, then team dashboard.
The team dashboard will show you all proofs that your organization owns.
Search for the proof you want to add an owner and click the i icon on the proof tile to open the info pane.
Click the plus icon to add an owner to the proof.