End Cap on throttle side of handlebar

[Rionna]

Hi, if this topic has already been addressed, please let me know where to find it. I was out riding yesterday and noticed that the rubber end cap on the throttle side of my handlebar was sticking out. It attempted to tighten the screw, but it appeared to be stripped and would not tighten. I don't know why that would be the case since I have never had any previous problems with it. Do you have any suggestions as to how I can fix it. Every time I use the throttle the end cap slips out further and I'm concerned it will eventually fall out. Thanks!