If this is a TE7 then the chuck will just pop off of the front end. You just pull the rear chuck sleeve foward to release the chuck. With the chuck off run the drill to see if the cylinder is bent. If you bent the cylinder it will wobble. If the cylinder is okay just order a new chuck. If the cylinder is bent then your best choice is to send it to Hilti and have it repaired by them. They have a ceiling on the amount the repair would be and you would get a warranty with the repair. It would be cheaper than you trying to buy the cylinder and replacing it yourself.
Hilti 1-800-879-8000

Glenn