Adding person to existing ADR

We have a Friday morning ressie for Tusker House for 3. If we wanted to add a 4th, what would we do? Or is it not possible?

Try calling WDW Dining my and see if they can add the additional person to your reservation. If they can’t, then call back and see if another CM can do it. If that is not successful, arrive early for your ADR and ask the host if you can add one more person. This should be easy to do, as a reservation for 3 will be taking up a 4-top anyway.