wordpress website Menu not working on my mobile and im technically layman in coding can anyone support to rectify

I'm not sure what happened or how it happened but one of our client websites mobile menu all of a sudden (at least I think it was all of a sudden) stopped working. I try to click on it and nothing happens (it's supposed to open a drop down) and I'm not sure how to fix.and im technically layman in coding can anyone support to rectify