Answer:
Sometimes debris can get stuck inside the fill valve causing it to refill your tank slowly. Please see the instructions below on how to flush out your fill valve.
If you perform the steps necessary to flush it out and it continues to run, then the entire flush valve will need to be replaced. The part can be purchased here.
if the fill valve will not turn off, shut the water supply off at the wall, remove the cap assembly and inspect for debris in the valve body seat.
Use an inverted cup over the uncapped valve body and turn the water on all the way for three or four seconds then turn off.
Do this twice to rinse out the valve.
Remove and clean the seal and the cap assembly then reinstall.
