Is this toenail fungus?
If yes, try to wear sandals to let your feet air out as much as possible at home. Throw out any shoes that don't fit properly or any closed toe shoes worn without socks that are bacteria traps. Always wear clean socks. Keep toenails trimmed short and straight as to prevent the toenail from getting bumped. Sometimes nail trauma can foster bacterial and fungal infections. Get a
cuticle pusher and scrape the funk out from under the nail. Always sanitize your implements (cuticle pusher, fingernail/ toenail trimmer, cuticle nipper, etc.) to prevent cross-contamination. I recommend physically washing and then using Barbicide. There is a
mid-size jar for nail implements, if you can find one. If not, any glass jar the implements fit in should work. Airdrying the tools and spraying with isopropyl alcohol is also recommended. For any personal reusable tools that are unable to be soaked, scrub with a nailbrush and spray with alcohol. Lastly, apply a topical treatment diligently and consistently. You can use something like
this. Be patient with this process. It can the better part of a year for the healthy nail to grow out. Follow the manufacturer's directions on the topical treatment. Good luck! :)