How do you assemble a Gamo hunter extreame air rifle?

If you disassembled it you may want to contact Gamo directly and see if they can help you with a diagram. Call 954-581-5822 Gamo Customer Service. Unlike Crosman who post schematics for all their guns and rifles, Gamo and Daisy does not. Your next best shot is to check the web for an "Air gun repair" shop and send it to them for assembly and repair.