Do you just want to conceal or do you want to ‘fix it’.
Forget nail polish, if you ever intend flattening it off you have two options. You can either build it up in layers using something like SP-system Ultravar 2000 2 pack polyester, , or you could repair it with a decent epoxy resin, SP-system, West marine.
You could use DIY store shit if you wanted, but they don’t set as hard as the stuff your bike is made of, they have no UV inhibitors in them and you won’t be able to flatten them off properly using rubbing/polishing compound.
if you want a perfect job you need to use decent stuff.
You could of course just try using some polishing compound and a reasonable hard plastic/rubber buff, but it’ll never get smooth if you build up with nail varnish.
I’d expect it’s not worth the £30 to do it right.