From the AppGallery home page:
1. On the menu bar, click Collections.
2. If necessary, click on the organization name and change the organization.
3. Click on the Collection from which you want to remove an app.
4. Click the 3 vertical dots on the tile of the app you would like to delete
5. Click Remove from collection. Doing so will immediately remove the app from your collection
Note: Removing an app from a Collection does not delete the app from your profile. To remove an app from your profile, you must delete it from the Apps screen.