My only suggestion is that you lay out a tarp. Then you carefully use a shovel (or some other special tool someone else may suggest) and dig up the top layer of soil where the grass and roots are. Put those pieces on the tarp. Then you dig down the soil as needed to reach the bottom of the sprinkler head. You can put the dirt on the tarp too, but put it away from the grass layer you dug up. Putting the dirt on the tarp keeps it from mixing in with your existing grass. After you've flushed the system and replaced and tested the new sprinkler head, fill the hole with the dirt from the tarp. Then "replace your divit" by taking the grass layer from the tarp and putting it back on top of the dirt.

That pretty much covers the technique. Use a rubber mallet to tamp the dirt as you replace it back into the hole. Then tamp the entire area with a sod tamp.