My leopard gecko needs to be fed?

I got a juvenile leopard gecko a few days ago and i need help. how do i feed him. I tried giving him crickets in his main tank but they hide under the substrate and in areas where he cant find them. A day after i got him i fed him in a separate tank where there was to substrate, just the tank and he was able to eat them easily and he got a chance to practice his hunting skills. when i fed him in his separate tank i noticed that he was breathing heavily and ran away from every time i saw him since. please tell me how i can feed him in his main tank. and ps i can ONLY feed him crickets.