Water stops the emulsion from being photosensitive. Water the screen with a hose and watch your image release, slowing adding more pressure with the hose. Hold it up to the light and look close to check if you can see straight through the screen. Water should be flowing through it. Be careful not to add too much pressure to the hose because it may wash out areas we don't want to wash out. Putting your thumb over the hose is fine, just don't use a pressure washer or hose head extension.
When you can see light through the entire positive of the image then you know all the prep work worked out perfectly and we're ready to print!