How to change the linked Instagram account?
When you click on the "Connect" button, the app will redirect you to Instagram and will, by default, select the Instagram account you are currently logged in (most of the time, this is your personal account).
In order to link a different account, open https://www.instagram.com and logout from your account (learn more about how to log out). Once you have logged out, re-link the app by clicking on the "Connect" button. This time, Instagram will ask you to log in. Simply enter the credentials of the Instagram account you want to be linked to the app.