In GoogleSheetB, confirm that the copy of Table3 arrived and is how you want it. You may want to rename it.
In the app editor, in Data >> Tables, update the configuration for Table3 to use the new copy of the Table3 worksheet. Change Source Path to GoogleSheetB and Worksheet Name/Qualifier to the name of the new copy of Table3. Then Save & Verify Data.
Confirm your app is using the new worksheet by making some data changes from the app and observing that the new worksheet is receiving those changes rather than the old worksheet.
If you want, you may delete the old Table3 worksheet from GoogleSheetA.
Note that there is no need to make any other changes to your app configuration. You won’t lose any column configurations.