I'm no expert, but here's what has worked for me in the past. The rooster will probably need several days of care, so be prepared. These are things that worked for my birds, I hope it helps this roo too. Isolate him in a cage in the house if possible and withhold all food for 24 hours, he can have a little water as needed. After he's been without food for 10-12 hours, check his crop. Depending on whether it's empty determines what to do next, the options listed below:
--If the crop is empty after 10-12 hours-- give him free access to water with raw Apple Cider Vinegar in it, use Bragg's brand, 1 tablespoon per gallon, but no food yet. After the full 24 hours is up, slowly start feeding him very SMALL amounts of soft food such as scrambled egg a few times a day, making sure the crop is emptying. Increase the food amounts and frequency over a couple days, then slowly introduce his regular feed. Keep checking that the crop is emptying. After a few days, he should be ok.
--If the crop is still full and firm/hard after 10-12 hours-- give him olive oil by mouth, about a teaspoon in his beak (or you can mix the oil with a tiny bit of baby food if he'll eat it that way on his own). Once the oil is in the crop, massage the crop, mixing the oil in with the crop contents. Then keep massaging every so often. Repeat the oil one more time if the crop hasn't shrunk after a few hours. Keep massaging. During all this, he can have free access to water with raw Apple Cider Vinegar in it, use Bragg's brand, 2 tablespoon per gallon. When the full 24 hours is up, if his crop isn't emptying, repeat the oil and continue massage. Once the crop empties, start feeding him very SMALL amounts of soft food such as scrambled egg a few times a day, making sure the crop is emptying. Slowly increase the food amounts and frequency over a couple days, then slowly introduce his regular feed. Keep checking that the crop is emptying. The crop should be back to normal after a few days. Note: the oil may give him runny poo, but should get better once he starts eating again.
--If the crop is still full, squishy and large after 10-12 hours-- give him free access to a strong mix of the raw apple cider vinegar (Bragg's brand) and water, 1-2 tablespoons per quart, make sure he's drinking this often, or give some by mouth, and gently massage crop, mixing the vinegar with the crop contents often. After the full 24 hours, the crop should start going down. If not, make the vinegar water a little stronger, and keep at it. When the crop does empty, keep him on just the strong vinegar water only for another 12 hours or so, then slowly start introducing VERY small amounts of soft food like scrambled egg (no dairy) a few times a day, and free access to the strong vinegar water. After a couple days, reduce the vinegar water to regular strength, 1 tablespoon per gallon. VERY slowly increase the food amounts and frequency each day for 3 or 4 days, then very slowly introduce his regular feed. Keep checking that the crop is emptying. Note: If there is no improvement in the large squishy crop after trying this for a few days, he may have a severe case of sour crop and he'll need a specific medication. It's called Nystatin and I think you can only get it from a vet.
I hope this helps. I'm no expert at all, but with help from BYC and trial and error, these things have worked for my birds. But like I said, if what he has is sour crop and it's really bad, you may need real medication (Nystatin) to save him. Please keep us updated and let us know how he's doing.