I don't own one, but have you read the manual?
(That's always a good place to start!) Boss products Manuals
'80 Rick 4001. '84 Fender Power Jazz Special, '05 USA Jazz, '11 USA Precision & MIJ M Miller Jazz. Zoom B3. GB ShuttleMax 12.0, GB Uber410, fEARful 212 sub, 2 x 15" cabs.