How to simple swap meshes by widget button?

You are using If Branches that doesn’t have a statement to the, and what is connected to false will never run.
Connect them like i draw out in this picture, you don’t need the if branches for what you are trying to do.

And again, watch introduction to unreal and programmering tutorials because this is very basic things, there are alot of free ones on youtube and cheap ones on Udemy.