looks like it is a press fit construction, very carefully line things up straight and press the top back into the tube. If you have access to a vise, it would make things "easier". Be sure to use some type of jaw protectors to keep from damaging the tube. And next time, run the telescope tube longer, put battery in, put on base cap, then gently run the telescope tube up till it is snug and not over tightened.
use the vise to push the cap into the tube by slowly closing the vise