U would screw it further into the red piece. That will allow the handle to spin a little further—up to that red piece / set screw. If that makes any sense.

If it looks anything like the kohler one it will look like this. https://www.kullysupply.com/kohler-gp77759-mixer-cap the little set screw attached to the red part is what I’m referring to. It helps adjust the hot water side so it’s not too hot.

There may be a small adjustment screw attached to the mixer cap that prevents the shower handle from turning a fraction of an inch. That small adjustment may get you where you need to be by allowing you to turn another 1/4 to 1/2 inch more.