From the rear of the model, for a right bank/turn, the right wing would be the "down" wing, and the aileron on that wing would be up.
Depending on the model, you might find that the ailerons need less down movement than up. We used to do this
mechanically years ago, and the modern computerized TX's usually have the capability to do this with with servo settings when you
have a servo and channel for each aileron.