Guitar Dual 2 Channel Footswitch Switch Pedal Latching Or Momentary Amp Parts 7625933708101 | eBay
DIY Two-Button Guitar Amplifier Footswitch
A special mini amp channel switcher/FX loop pedal (When you actually only use 1 of the 2 functions and the other is always on or off) Details in comments. : r/diypedals