As rightly mentioned by my fellow dentist .. it is AN ULCER .
Next Steps
1) Apply Orasore / Metrogyl Dg gel / Ornigreat gel on it ... thrice a day ( after meal - do not rinse or take liquid for atleast 10 -15 mins, so that it can do it's work .
2) you can also use sensigel or mucopain if it pains while eating .. in that case apply the gel before meal ..this will numb the area
3) Avoid hot and spicy food for few days , so that it can heal ..
4) use soft / ultra soft toothbrush & be little gentle while brushing
Health Tips
Do not touch or try to scrape it .
It will heal itself 2-3days