device still shows up even after deleting

Somehow or another, one of the iMac 21.5" computers from my college's library is showing up as one of "my devices". When I try to remove it from my account using the iCloud preference pane on 10.15.6, it never actually goes away.

Since I won't have access to the machine for an unspecified amount of time (due to covid), there's no way I can physically go delete it off of that machine. Is there a way to get rid of it without actually having to have that machine in front of me?