How do I swap players??

hi, i need help, cant figure out how to swap a human with a fish (both playable) when colliding with water (and vice-versa). Completely different playable characters

any help would be helpful

I would do it with a global variable, you can set it to 0 or 1 depending on who you are playing as. Then your events for movement and such can have conditions like var=0 and var=1. In a basic sense you could set the variable to 1 when you collide with the water, and back to 0 when you are not overlapping the water.