Hiya, I used to bite my nails really badly but then I cut my finger and had to wear a band aid on it for a few days and didn't even try to bit that nail so I tried putting one on each finger. It sounds a bit silly but it worked, I think it just broke the habit and whiloe I do still bite them every so often I don't do it to the extent I used to. Obviously this isn't getting to the root of the anxiety but it helped break the cycle.
I tried the clear nail varnish but used to just bite it off, it tasted gross but the feeling of biting my nails was better, lol.