You have to push the centre knob when you put power to the unit, hold it until the screen goes through it’s start up. Release the centre button. Push the left button three times which brings up the set up window at the bottom. Rotate the centre knob to each setting to be trimmed. When you get to the value to be trimmed, push the centre knob, trim then push the centre knob again. Move to the next value and repeat.
If I remember correctly this is explain fairly well in the install manual.
Good luck