What is a good OTC medication for psoriasis of fingernsils?

See below. Fingernail psoriasis may be just the tip of the iceberg: psoriasis can attack bones/joints (psoriatic arthritis). Better to see a rheumatologist or dermatologist for good evaluation & treatment options.
There is none. Nail psoriasis is one of the more challenging aspects of psoriasis to treat. There are not topical medications that will help the problem as they do not go deep enough. There are other options that included oral medications like soriatane, Methotrexate or the biologic medications (enbrel, Humira (adalimumab) etc). Finally, dilute steroid injections into the nail fold will help but they are very painful.