The first step making an N64 Controller pipe is to unscrew the screws on the bottom side of the controller. There should be 9 screws in total.
The second step is to go to your local plumbing supply. You might want to bring the top part of the controller with you to the store as you'll need to double check the size of the fitting you'll need to use as a bowl.
What you're going to look for in the plumbing supply store is called a PEX fitting. The PEX fitting will be 1/2"