This forum here is a user-to-user community forum. If you face any challenges with licensing, please contact Adobe Technical Communication Support at tcssup@adobe.com
The standard process for a single-user license is to Choose Help > Sign out (colleagues@email.address) in the FrameMaker menu on your colleague's computer. Then sign in with on the new computer with the same credentials (Adobe ID).
However, as your colleague has resigned, you will need to migrate the license to a new account. For this, it's best to contact Adobe Technical Communication support.