Spa pump/insinkerator Chrome plastic top DIY Replacement Pneumatic Air Switch  fits 32mm hole,  top diameter 45 mm, 28mm hole size available[or easy to just file out hole to fit 32mm], no danger as switch is air operated. If your old button has no access underneath to undo nut, just grind the top off, let it fall inside, then fish out air pipe with coat hanger

Bobs tips: before fitting air button to air hose, blow into hose with your mouth making sure pump turns on and off, if not the tiny air hose may be blocked with water inside, the micro switch on the motor may be not working, no power supply[check the power point and fuse/circuit breaker], or the pump is kaput. If the pump hums it could be seized with a hair pin, piece of plastic toy, or even bad bearings. First thing with a seized pump, pull the front off and see why it wont rotate