Using warm water, forcefully spray the screen to remove the ink before it dries. If it dries on the screen, use mineral spirits to clean off the ink.
With a nylon bristled paint brush, apply some stencil remover to the photo emulsion on both sides of the screen. A little goes a long ways. I have heard some people suggest using bleach to clean the screen. But you will end up having to make 3 or 4 applications, and bleach is harsher on the screen thus shortening it’s life. The stencil remover only cost me about $10 for the bottle, and it is going to last quite a while.
Using a nylon bristled scrub brush, lightly scrub the stencil remover into the screen. You should see the photo emulsion disolving.
Simply spray the photo emulsion out with a forceful spray of warm water. Apply more stencil remover if necessary. Degrease the screen using trisodium phosphate or dish detergent, rinse thoroughly, and allow to dry. The screen is now ready to be recoated.