After spending some time in your zone, which now has a name and is familiar to you, add minor annoyance or distraction and return to happy place. Imagine a fly buzzing past (a minor annoyance) and then return to your happy place. Practice, add slightly greater annoyance and return to happy place.
As a trigger to return to your happy place you can use the name of the place, or a song or phase that connects you to that place. You can also use a physical cue (snap your fingers, pump your fist, twitch your nose like bewitched). When you are stressed or annoyed, try using the cue to take you away.
Re-focusing can be as simple as reminding yourself of your happy place. However, you want to have more than one tool at your disposal in case that is not enough to get you and your game back on track.