Seems nothing serious as you are undergoing orthodontic treatment the most common problem is maintaining oral hygiene.
It might also be so that some sharp food has caused the injury and now a scab is formed in that area.
Please don't hesitate on proper cleaning of the area.
Next Steps
Use mouthwash and do warm salt water rinse after every meal. It may go on it's own.
Health Tips
Don't use any foreign object to touch the area with as the chances of infection might increase.