Does showing the ad again to people who already saw it work better than reaching people who do not know you?

No, showing it again does not work better as a rule: if the shift has no new guests, you need people who do not know you. Yes, the reminder works, for a few days, if they already saw the dish and did not write. Count whether this week’s bookings are new names. The same people are pressed and the neighbourhood that walks past the door never sees the dish. The week’s split, reminder or new people, with the bookings from each.