This is the part you should read:
If you suspect impacted crop, administer two eye-droppers full of mineral OIL (NOT MINERAL SPIRITS!) by forcing an eye-dropper down the chickens gullet, and massage the hard lump between your fingers to soften it up and help her pass it. Repeat if necessary the...
I found this online:
People often suspect something is wrong with a chick or chicken if their crop is full. In the case of chicks or juvenile birds this is usually normal as they will eat quite a bit during this fast growth period. It often happens with full grown chickens as well and is...
I read that massaging their necks is helpful. Try giving more cooking oil. Make sure he drinks water.
Is there anyone out there at BYC who can give better advice?