To disconnect apps:
- Login to https://apps.intuit.com/
- Click on My Apps
If you have multiple QuickBooks Online companies, select the company with the app you would like to disconnect.
- Click Disconnect under the app you would like to remove
You can do the same from within QuickBooks Online on the Apps tab.
The Sync with Square app is absolute swill. Completely useless, creates far more work than manually adding transactions. It's hard to believe the Intuit team created an integration that doesn't sync customers, products or partial payments. And it's terribly documented too. You should fire the developers.