Like Ria says, first of all what size is his cage?
I had to try various different chews with my Luna when I first got her to stop her bar chewing, The things I found that helped the best were water hyacinth mats and carrots like these
https://smile.amazon.co.uk/gp/produc...?ie=UTF8&psc=1
I tie them to the bars where she would chew.
Also, I found that if I switched the lights off and pretended I wasn't there, she would stop chewing and merrily go abut her way on her wheel. So, because of that, if she chewed her bars, I would try and deter her and then wait till she was distracted with her wheel for example before i let her out. so she wasn't associating chewing her bars with being let out. This is not me saying ignore the bar chewing, you still need to work out why your hamster is doing it. When a hamster chews it's bars, I look at it as they are trying to communicate that something isn't quite right for them and then we have to work out what that is is. It took me a while and I felt awful when Luna chewed her bars, but i got there in the end.