Go to your Host panel and open Table management.
Select a date and and find the reservation which you'd like to have tables swapped.
Then, filter the time at the top center of the screen.
Click on the Reservation. Click on its assigned table and hold for a second or two and drag it to another table.
If the table is empty, you will be asked if you want to move the group
or add new table - click on Move group:
Swapping busy tables
If you are swapping two busy tables, simply drag one table to the prefered one and the groups will be swapped.
After swapping: