You may be able to disguise mild nail changes by scraping, filing, or polishing your nails. Try to keep your nails short. Avoid injury to them as much as you can -- that can make things worse.
For more serious problems, your doctor may give you corticosteroid injections in your nail bed.
Many people with psoriasis have a fungal infection in their nails (called onychomycosis). Ask your doctor or dermatologist to see if you have it. If so, treating the fungal infection will help your nails.
If you have severe psoriasis or psoriatic arthritis, your doctor may want you to take a prescription medication that affects your whole body. That should ease nail problems, too.