If you're dealing with an overhead spray irrigation system, first determine where the leak is coming from. If it's coming from the top part called the nozzle, unscrew the broken nozzle and then screw a new one on. In the case of drip irrigation, determine where the leak is coming from first. Next, locate the pressure coupling. Cut the broken drip if it's not severed all the way through and put the pressure coupling on both ends. Push on it, and it'll be good as new.