Since the egg sack is completely absorbed, just keep him very warm, like at 97 to 99 F for the next one to two days.
He won't have to eat for the first 48 hours after hatch, and might just need to sleep and keep warm.
Hopefully, about 24 hours after hatch (well, his assisted hatch), he should start looking a bit better.
Once he is looking better, you can sprinkle some chick starter on the floor of his brooder, and add water that he has NO risk of falling into and drowning in.