How do I unlink my Insta from someone else's FB account?

Hello,

My Instagram account is linked to the wrong FB account...one that I do not manage. I'm not sure how this happened, but i can't find any instructions online for my specific issue.

When I go to Accounts Center, the account is NOT listed there for me to remove. I simply want to connect the correct account, but can't unlink the existing one. NOTHING i try works, and again...the basic instructions i find over and over online will not work for my situation.

To reiterate...when I go to Accounts Center, the account is NOT listed there for me to remove.