Turn off the water supply to the toilet
Remove the tank lid
Check the flapper for wear, warping, or debris
Clean or replace the flapper if needed
Check the chain length and adjust it so it has slight slack
Inspect the fill valve for damage or continuous water flow
Adjust the float level if the water is too high
Replace the fill valve if it is faulty
Check the flush handle for sticking or improper alignment
Inspect the overflow tube for cracks or overflow issues
Make sure the tank water level is set below the overflow tube
Replace worn tank parts if necessary
Turn the water supply back on
Flush the toilet and confirm it stops running
Repeat adjustments if the toilet still runs