To relink your Instagram account with your Facebook account and YOUR account only:
Go to your Instagram profile and then tap Edit Share Settings > Facebook
Visit Facebook's app settings to revoke access to Instagram which will unlink the wrong Facebook account.
Just tap the Facebook icon again on your IG and enter your login information to link the correct account.
To relink your Instagram account with your Facebook account and YOUR account only:
Go to your Instagram profile and then tap Edit Share Settings > Facebook
Visit Facebook's app settings to revoke access to Instagram which will unlink the wrong Facebook account.
Just tap the Facebook icon again on your IG and enter your login information to link the correct account.