When you use the SYNC section, the system will prompt you to connect via Instagram and it will connect to the primary account you're logged in on instagram.com (the website, not the app).
If you have the wrong account under SYNC, you can fix it following these simple steps:
From the same browser you use for Lnk.Bio, head over to instagram.com
Log Out from the current Instagram account and Log in again with the correct one
Go back to Lnk.Bio SYNC section
Tap on Disconnect as shown below
Connect again with the correct account