It depends. Mother says the cal-mag her doctor prescribes gets rid of hers. They are a lot bigger and deeper than mine were. I had many small ones that went away when I started taking Iodine. Some parasites may gobble up B-12, but others won't. Being high in B-12 doesn't necessarily mean you don't have parasites.
Human beings are a genetically diverse species and there are thousands of parasites looking for hosts. Your genetic make up will make you vulnerable to some and invulnerable to others. Getting well is an individual matter.
If you google "ridges in fingernails" and mineral deficiences that cause ridges in fingernails" you will know where to start supplementing. Listen to your body. It will tell you what you need.
Posting a message here will also net you a lot of good information. Apparently at least one person believes there is a relationship between B-vitamin deficiency and parasites too. If more people chime in and say they got rid of ridges on their fingernails with B12, it is worth considering, unless you can already rule it out because you know your B-12 is high.
On the other hand, how do you know you don't have a parasite that is preventing your body from utilizing the B-12 in your system? Is there such a thing? I don't know.