I applaud you to take charge and try to give this BP a second chance.

The first thing I would do is take him to an herp vet to have a clean bill of health.

The second thing I would move him to a 41 quarts tub with 2 identical hides (avoid log hides) temps of 80-84 on the cool side and 90-94 on the warm side and 50%-60% humidity.

Make sure you have proper measurements of your temps and humidity this mean having digital thermometer/hygrometer.

Once you have done all that leave him completely alone for 1 to 2 weeks no handling.

Once that time has passed I would suggest offering small preys and I would start off with rat pup and slowly move to small rats (45/65 grams) which is the biggest size you will ever need to feed him.