We found an older article about cleaning sprinkler heads here: https://www.doityourself.com/stry/cleaning-sprinkler-heads
It gives several helpful tips in an 8-step process, including this excerpt:
Step 1 – Lift Sprinkler Head
A sprinkler head is fitted inside a sleeve. It remains in this sleeve when not in use and then lifts up out of it in order to spray. You need to lift the head out of the sleeves so it is in the position it would be in if it were running.
Step 2 – Remove Sprinkler Head
Unscrew the head and remove it from the sleeve completely. If you’re having trouble removing the head, you can run the water and let the sprinkler lift on its own. The added water pressure pushing against it can make it easier to remove, albeit messier for you.