Best to purchase the entire guts of the toilet this included the rubber stopper,
handle and chain. then hire a local handy man (ask your local hardware man for referrals) Believe me its the way to go. A total toilet tune up should last 10 years.
You can buy an inexpensive kit that has everything needed to replace the flush mechanism in your toilet tank. It's easy and directions are on the package. That should fix your problem.
Hi Sheryl Hope this article helps https://www.familyhandyman.com/plumbing/toilet-repair/how-to-fix-a-running-toilet/view-all/
You don't need to replace the "guts" or a repair kit. First check to make sure the flush handle is not binding when after flushing. If it is loosen the nut a little. Make sure there are at least three loose links on chain when the flapper is down. If the flapper feels hard or is warped from age that is the only thing you need to replace.
ask william !