I just figured it out. Here is what I did step by step on my phone.
1. click the settings icon on instagram (top right)
2. Scroll down to "share settings" under preferences.
3.Click facebook
a)if its linked to the wrong account and you get the message saying that youve already authorized instagram.... simply click in the address bar and type Facebook.com
b) you should be already signed in to the "wrong account" simply sign out and sign back in to the account you want instagram to link to
4. Once signed in go back to instagram and repeat steps 1-3
5. It will now asked to link to the account you sign in to.
VOILA! hope it works for you too