Toto Run on problem

I have 3 Toto toilets in my house that have been working well for 2 years
now. One of them has recently developed a run on problem. When I flush the toilet, it will continue filling water past the overflow and run on until I
manually open the tank and push the inlet valve mechanism back towards the
flush handle and then it will shut off. This problem started out sporadically
but is happening now with greater frequency. What should I do?

There are instructions here for some of the fill valves

Key

Thanks for the instructions but how do I get the key out?

The key just holds the adjustment. Unless you had changed the positition, there would be no reason to remove it.

If you do want to remove the key, you sort of push and then pull it out.
You push it to get it past the pins and then you can slide it down.