Although a bent barrel doesnt mean bad accuracy, if its so bad as to be unzeroable then it can be bent back, if its a break barrel then no doubt someone let go of barrel whilst cocking
You need to remove barrel (if break barrel) and put breech in a decent vice (protected jaws) then use a piece of pipe over barrel to where the bend is and firmly but slowly give it a nudge until its straight enough to be used again
If this was an expensive gun then I would offer different advice
Baz