Help! Air Bubble in crop from bad frost bite?

Got a new rescue chicken two days ago. Just got time to post my question. Not sure what he is. But maybe a year or so old black/blue andalusian?

I got him because he got left out over night by accident. It was about zero to -10 below. Previous owner though he was dead but he woke up after being brought inside. I don't think he has eaten much in 2 and a half days. His crop, wattles and under his head (on the neck) were extremely swollen. He could not move his head much.

I have him crumbled baby aspirin and water through a dropper. The swelling has gone down in the past two day a lot. He now tries to move his head down and peck at corn. Its a good sign! One weird thing was that when he was really badly swollen he drooled a lot? The drool looked very thick, much like mucus. And somewhat discolored. He made minor rasping noises. But now much now.

I've been giving him lots of water through a dropper. He ate some corn and a bit of table food.

Ive noticed as the swelling went down on his head, he developed an air bubble around his crop. I can see some of the bubble near the top of his shoulder and then down his front. I would describe it as large. Maybe half the size of a baseball? I applied some pressure last night (very gently) and it went down. I could hear the chicken letting the air out. But the bubble inflated again.

What is the bubble? Has anyone heard of this before? Is the bubble from breathing difficulties or is it from an impacted crop?
What can I do to help the air bubble? He is separated, With access to water and food. Warm enclosure. I have gave him olive oil to help anything pass in the crop. His comb/wattles are getting better. I applied neosporin/lotion. I took him because I thought I can nurse him back from frost bite, but the air bubble is an unexpected problem.

Sorry for the long post.

Thanks!