I third getting a plank to use flat on the ground. The problem with not being able to lower the dogwalk means it reduces your training options, though you can get through this. Merlin has never much liked the contact equipment and he has fallen off too, at one point last year he simply started to avoid the dogwalk like the plague at my old club. The important thing is to keep building confidence.
Merlin used to have big issues with the a-frame, my old club didn't have one, so my only option was to buy a smaller practice version for my garden. Even then just trying to lure him over it he was refusing it and running away. So I dropped the entire thing to the floor and at first just clicked him for going near it. Then I clicked him for putting his paws on it and building up to him walking and then running across it. It was not designed to be used on a lower setting, so I got inventive, bought some chain and bolts and began raising it literally inch by inch off the ground. By the time it was back at full height Merlin didn't have a care. I also was able to work on his running contacts. The a-frame remains his best piece of equipment and he never misses the contact.
So, definitely try to have a plank at home. A short one you can even use indoors and raise it up on books, once he is happy stepping on it, to get him used to being off the ground.
At club I would begin by just rewarding him for being near the dogwalk. Maybe let him watch other dogs going over it to see it is 'safe'? Then I would feed him treats that were placed on the dogwalk, again making it a good thing. Then lure him to put his paws on it. I would gradually encourage him to climb on, even if it meant lifting him off when he became uncertain (I would rather lift him off then have him turning around and walking off himself, which can cause him to fall off again). I would keep asking him to climb up a little further and further.
Some trainers don't like you lifting dogs off equipment, but if it is a case of that or dragging him over it, I would much rather lift him off. I would want him to choose to go up, not be forced.
Basically this is going to take time. Once he has got back to running over it, I would ensure he always runs on it from a straight line, as angled entries onto contacts put a dog at more risk of falling off, and you don't need that right now. You can worry about angles when he is confident again.
I'm sure he will get his confidence back soon. If Merlin can, any dog can!
