What should I do if a coworker is telling lies about me to my manager?

I had a one-on-one meeting with my manager and the first thing that she brought up was to tell me to not play first-person shooter games at work when I’m not on my break and that somebody had told her.

I asked her if I was the one who was playing the video game and she didn’t deny it, but just reiterated that somebody had told her that I did.

I also agreed with her that people shouldn’t be playing video games while at work.

I am not the kind of person to even play video games at work, even on my break. And I don’t play first person shooter games either, so everything was so confusing.

I wasn’t even sure who could have told my manager, but the fact that my manager had to tell me not to do that is honestly making me look bad and frankly I don’t even know what to do about this since it’s clearly false and there’s no evidence that I did play video games at work. And I don’t even know who lied about this to my manager, so it makes it even worse knowing that there’s a coworker making up obvious lies about me behind my back.

I think looking back, I should have told her that I have never played first-person shooter games at work, let alone video games in general at work. But I was too shocked at that time that I didn’t do that since I found it too ridiculous of an accusation and didn’t think she was being serious.