Setting Level and Pan is an Instrument Assign function located in Sound Parameters.
Use the following procedure:
1) Press EDIT.
2) Cursor to [PATCH] and press ENTER.
3) Cursor to [INST] and press ENTER.
4) Cursor to [SOUND] and press ENTER.
5) Cursor to [Level] for volume or [Output assign] for panning.
6) Use the VALUE buttons to change the selected parameter setting.