I have a newer toilet that does not have a ball mechanism, but a floating device and it is not floating to the top to stop the toilet from running. What are my options for fixing?

I'd like to ask a question or two before figuring the fix. Is the water level reaching the top of the overflow tube and still running, That would be a float adjustment. If the toilet keeps running but never reaches the top of the overflow then it sounds like the flapper is not making a seal. Do either explanations apply for you.