I did bhs on beam for 3 or so years before I had to leave the sport and never got over my fear of them. My main problem was that I was so scared of them that when I got to the high beam I would totally change the way I did the skill and just chuck it over- which would not always end up so well (missing hands and crazy crashes). So I think the most important thing is to be comfortable enough with the skill to be able to do it correctly on the high beam, if not totally confidently.
Do you have a medium height beam in between the low and high beam? You could try making a certain amount on the low beam each day (I would say at least 10) until you feel totally confident, getting your hands on each time. Once you feel absolutely confident with that stage, move to a mid-sized beam and repeat the process. If you notice yourself changing anything, head back to the low beam. Once you feel totally confident on the mid-sized beam, head to the high beam. You could try throwing a sting mat over the top if you're allowed, if not you should be confident enough by this point to feel okay going for it on your own. If not, head back to the medium beam for more reps. Don't rush the process, and don't be afraid to go back a step if you find yourself getting so scared you're changing how you do the skill. It's a process, and not always a quick one, so take your time. Rushing through it usually just results in fears at some point down the road.
Even when you do feel comfortable with the skill and do it well most of the time, freak things can happen, you just need to be sure enough of yourself that you can get back up there and correct the problem. Good luck! It's tough to battle through mental blocks like these, especially ones that have some merit to them, but if you had the skill once before- and good enough to do a bhs series- I have full confidence that you'll be able to get it again!
