I'm sorry you don't have access to a vet. Your bird's injury is probably very painful, the best thing you can do at home is provide a more comfortable place for your bird to stand. The grate may be irritating the foot and making the injury worse. I would clean and sanitize the cage and the entire area that the bird uses. Cover the grate with clean newspaper or a towel, provide perches at a lower level in the cage. Natural perches are better for a bird's feet. The foot should wrap around 2/3 of the perch, the toes shouldn't touch or overlap. 1/2 inch to 1 inch in diameter perches are about right for a cockatiel. I wouldn't use dowel perches or any scratchy perches while the foot is so irritated. It's important to keep the wound clean, you could soak the foot in a shallow dish of Epsom salt solution, one teaspoon of Epsom salt to one gallon of warm water. After flushing with peroxide and letting the area dry, I would rub the wounded area with vitamin E oil.
What kind of diet does your bird have? Vitamin A deficiency is linked to foot sores. Adding vegetables like sweet potato, carrots, dark leafy greens would be helpful.
I can't advise you to use antibiotics, especially orally, only a vet can prescribe proper dosages.
