Simple check:
Short out the two solder pads momentarily with a short length of wire or even a screwdriver blade. If the function operates it means the switch is faulty.
The reasoning:
That kind of switch normally has no connection between its two pins, when pressed they are bridged (linked together). The electronics at the other end of the cable has no notion of what caused the linking so if something else does it successfully but it wasn't the switch that did it, the function would still work as expected.
The fix:
A new switch - they cost pennies and are easy to find but be careful to get one with two pins, most have four, one in each corner and ensure the height of the plastic button is the same or it won't line up with whatever pushes it.
Brian.