I've no experience fitting this part, so take this answer as a possible suggestion. I've taken a look at the part online, and to me, it appers to have two delta shaped lugs on the protruding shaft with a seating groove behind. My guess is that the switch pushes into place from behind and this two lugs lock it into place. On that basis, i'd suggest using a pair of pliers or similar to compress both lugs at the same time, whilst pulling the switch backwards. Failing that, if you have a new part, maybe try destroying the plastic switch body a little bit at a time until it gives way, whilst being careful not to damage it's mounting point.
Would be useful if you could post a reply on how you managed it in the end for future reference.
Rupert, March 2020