How do you repair a Model no 799.19052 bb gun?

This BB rifle was made for Sears by Daisy air gun company. It's really a model 1894 and possibly one of the hardest BB rifles to repair. I suggest you look online

for "Daisy air gun repair" and locate a shop near you to have it repaired. There are shops that make a living repairing outdated air guns and rifles.