If you have reservations assigned to tables and they do not light up with the reservation in the time set up beforehand then you may have old reservations left on past dates that were never cancelled, sat or set as no show.
In order to check for old reservations, tap the date on the top of the reservations tab and scroll back 2 days at a time to check for old reservations which need to be removed by cancelling them.
If there are only one or two tables in question then you can tap on the table and tap the party name under "party currently assigned" which will bring up the details of the reservation including the date. Next scroll the date dial back to the old reservation date and cancel reservation.
Once old reservations have been cancelled, the tables should light up automatically with present reservation.