The Particle V1 uses a standard 3PDT latching bypass switch.  To replace a broken or worn out footswitch, follow the wiring in the diagram below. 

You can also use the Mammoth Electronics Large 3PDT Wiring Board (4Site LRG3PDT) to make the wiring easier.  To use the Mammoth board, cut the Particle ribbon cable by the switch board.  Carefully separate and strip each conductor in the ribbon cable, then solder the ribbon cable to the 3PDT wiring board by lining up the square pads.