Yep, wash in salt water if you can, dry it and then apply the tea tree oil. You can find it in most drugstores here in Canada. Costco even carries it. Its an herbal remedy that lots of folks use for a lice treatment, acne treatment and as an antifungal treatment. Athlete's foot is a fungal infection and tea tree oil works very well on it.
With all due respect to PF's expertise, we found the yogurt treatment makes the athlete's foot FEEL better but it doesn't work as fast. Its a fungal thing so you need an antifungal cream. OTC preps for yeast infections work too, again, more slowly than the tea tree oil
My niece had the worst athlete's foot I've ever seen and it took a LOT to get rid of it. I had a less serious bout of it and the tea tree oil gave me relief in 24 hours and it was completely gone in 72 hours.