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You didn't load your pic, or do an intro, so don't expect much.
If it's a dent in the sheetmetal, paintless dent removal (PDR) is the accepted practice. If it's the plastic lens, buy a new taillight assembly. The trim could maybe be fixed and repainted, but that's a lot of trouble.
Any bodyshop will give you an estimate and options.
Is that the only damage? From the pic it just looks like a chip, in which case you get some of that scratch fix touch-up stuff from napa or wherever and follow the instructions.