First thing to do is is to cap the fitting so dirt does not enter. The fitting appears to be connected to swing pipe which is very flexable. Dig back and expose the swing pipe for about 12" or so. this will give you room to lower the head a couple of inches. If the swing pipe is short where you do not have much flexability, you may have to dig back to the line that feeds it and lower it a bit. Put teflon tape on the fitting before replacing the head.