If you need to connect an Instagram Business account related to another Facebook account, then clear cache and browsing data for the Safari app:

• Go to your phone Settings → Find Safari app → Click ‹Clean History and Data›. You might be logged out from the Safari accounts on the device, but your auto-filled passwords will not be deleted
• Go to Content Office → Office → Projects → Choose a project → Connect → Professional → Click ‹Continue with Facebook› → You will be navigated to the Facebook login screen where you can enter a username/password for another Facebook account and proceed authorization