Just leave it be, it will be fine and will continue growing as though nothing has happened. Cannabis is one tough and resilient plant and unless it droops immediately after snapping, all will be well. There is no need to do anything, in fact trying to straighten it out could cause even more damage and be fatal to the part above the snap. No need for special treatment either, just continue exactly as before when it comes to water and feeding.
Hope this helps, Organoman.