In the center section, are individual bypass buttons labeled CH 1 & CH 2 (LEFT/MID & RIGHT/SIDE).
These bypass buttons are large toggle buttons with two states:
When you press the left bypass button, it turns on all four bands on the left side of the screen. No matter if they're set to LEFT or MID mode.
Pressing the right bypass button activates all bands on the right. Whether they're in RIGHT or SIDE mode.