How do I make one of my sprinkler heads that is currently running in zone 5, change so that is runs with zone 6?
Basically, are you asking how to combine zone 5 & 6? If so . . . Do you have a master valve or pump? If not, you should be able to take the hot for zone 5 and put it on zone 6. Depending on their locations, you might be able to connect the zones together. With a pump or master valve especially, I would first be a bit concerned about too much power draw. Secondly, depending on the number of heads, type of heads, and distance, I might be concerned about pressure.
I’m reading this as wanting to move only 1 head from zone 5 to zone 6. Only way to do that is re-pipe that sprinkler to tie into the zone 6 piping. Nothing you can do within Rachio, unless you are willing to combine the whole zone like @Thomas_Lerman said.
Oops, I saw “a sprinkler head” in the title, but missing the “one of my sprinkler heads” in the body. So, I must have interpreted the body as “one of my sprinkler zones”. If you are talking about moving a single head, @tmcgahey has the answer. Unless we are both misunderstanding or that one zone has one sprinkler in it (seems unlikely). Over the past few years, I have split a zone into 2 and 2 other zones into 3 for better coverage and pressure (which changes throughout the year). Definitely re-piping (luckily pretty minimal) and in my case adding valves & wires as needed.