Need help- rocker stud has stripped

Hi guys, im in a bit of mess

Im only a very novice mechanic so bare with me.

The thread for the rear of 3 large rocker shaft studs has stripped, I was tightening the rocker cover back on and it came loose.

When I removed the stud I noticed a previous owner or garage has helicoiled the thread as the helicoil come out with the stud,

How do I repair it? can you re helicoil a thread? can it be done in situ or so you have to remove the cylinder head?

At the moment obviously the vehicle isnt driveable as the valve clearence at the rear are miles out due to the above.

you can helcoil the thread with head in situ ,just try fitting another its not unknown for the coils to unscrew especially if not fit fully, there are few different makes and different types

If the helicoil thread in the casting is OK, there's no reason why you can't put another in. If it were a head bolt I'd be a little apprehensive, but it should hold in the application you describe. I have even re-used old helicoils in situations where I didn't have new ones to hand and they were fine. Perfectly good enough to hold the manifold on an Austin 7 block, anyway. Not best practice but it kept us going.

James beat me to it.