These sores are caused by the braces rubbing against the lining of your mouth when you talk, eat and smile. Not everyone gets them. To let a sore heal, we need to isolate whatever is causing it – the bracket, hook or archwire that is rubbing. In these cases, wax is the best remedy. Orthodontic wax is soft like modelling clay, transparent and completely biologically inert – it's perfectly safe if you swallow it. Press a small ball of wax onto the part of the brace that is causing the sore and leave it in place until you next brush your teeth. Then replace it with a fresh piece, and keep doing this for a few days until the sore has healed. You don't have to put anything on the sore, but if you'd like to, ask at the pharmacy for a treatment for sores caused by braces. Not every sore in the mouth is a mouth ulcer (aphtha), and treatments for mouth ulcers are different from those for this kind of sore.
This answer is for general information. Your own case needs an examination by an orthodontist.