Bathtub plumbing question please help?

The diverter valve is not shutting off the water flow to the spout. This could be a washer problem or a washerless valve problem - like o-rings. Remove the diverter valve and take it to a hardware or plumbing store and get the correct repair parts for it. You shouldn't need a plumber for this repair, but if you are totally lost as to what to do a handyman or plumber could fix this problem for you.