Turn off the water supply valve behind the toilet
Remove the tank lid
Check the flapper for wear, warping, or poor sealing
Replace the flapper if it is damaged
Check the chain length and adjust it so it is not too tight or too loose
Inspect the fill valve for leaks or malfunction
Adjust the float if the water level is too high
Lower the tank water level to the marked fill line
Clean mineral buildup from the flapper seat and valve parts
Replace the fill valve if it continues to run
Check the overflow tube for cracks or overflow issues
Turn the water supply back on and test the toilet
Replace the flush valve assembly if the problem persists