How many? You can lure them out with salad, and that will also give them something to eat rather than your dragon. They chew more than bite, and since dragons skin is tough they will go for the softer spots like eyes and soft skin. The damage may depend on how hungry the crickets are.
Try to grab them out as you see them or lure them with some food. They might not come out till after dark. If they aren't hungry they might not bother him but its better not to have them in there pooping and annoying him.
I had some success with the cricket keeper tubes, although toilet roll middles might work just as well. Cover the cricket with the tube and it should run up inside, then you can take it out and put it back wherever you usually keep them. I also found it helped to take any furniture out the tank while catching them. Less places to hide! They are a pain. I'm feeding reptiworms at the moment and I don't miss catching leftover crickets!
I usually put a small plastic baggie on my hand (like you do to pick up dog poop) and scoop them up that way since the bag covers the space between my fingers and they usually get trapped in the folds of the bag. I've also had success leaving an empty tube from my cricket keeper in the vivarium, since crickets like dark spaces and will often climb in on their own. Just keep checking periodically so they don't crawl back out. If they've already found a place to hide in the vivarium you might have to coax them out so they'll find your tube.
And I'd definitely leave some veggies in there for something to chew other than your dragon.
Best way I've found to remove them is to provide them with a dark place to hide that the dragon can't get into. I have 4 black tubes that came with my cricket keeper. Whenever too many crickets go into Elvis's viv I just lay the tube on the floor of his viv's cool side. I take the tube out in an hour or 2. Usually the crickets have gone into the tube to get away from the heat, light and Elvis. He's full of their brothers and sisters, but they don't know that LOL.