there is a nice youtube video on it. just youtube force feeding frog.

i used a credit card. i picked up my frog in a wet paper towel and held it inside that. it was squirming so i had to squeeze a little. but not too tight. it took me a minute to get a good hold on it. after i got a hold of it with one hand, i used my other hand with a cleaned credit card and used the corner to gently push into the frogs mouth and open it up. then had my girlfriend throw a cricket in there. it swallowed it like normal. some people say syringe feeding but i suggest having a vet or someone with experience show you how because you can accidently get it into the frogs lungs and cause problems. if you dont have anyone to help you. try using your thumb to hold a cricket ontop of the credit card. then when you get the mouth open lift your thumb up and let the cricket slide in. i would only do 1 cricket and see where that gets you. then just put him back in the tank. the key to doing it is to keep your frog under as little stress as possible. good luck and let me know how it goes