You might be able to heat the dent with a hair dryer and bash it out. It will leave a noticeable mark where it was dented but this method has worked for me in the past (this comment assumes it's plastic rather than metal).

If you don't need a zippered case, you might be better off with Shield Lock 2 76 cm spinner that's also on their website for £125. Seams on Zips on cheaper cases tend to be more prone to failure.