ok this one is super duper easy

where is the red switch at?

When you get to chocolate island, beat the ghost house and the next two levels. When you
beat the second one, you will see the game making a circle path. Go back to the same level
that you just beat and find the key and keyhole. That will grant a path straight through
the circled path. Win the next levels. Eventually, you will gain access to a Bowser statue
that leads you to Bowser world. And you've beat chocolate Island!