Based on the photographs it looks like a small traumatic/ irritative ulcer,erythematous traumatic lesion,most likely from cheek biting, rubbing against a sharp tooth,or irritation around the wisdom tooth/ molar area.
Next Steps
if a sharp edge is present,smooth/polish it or treat the offending tooth as appropriate.
Avoid spicy, very hot and acidic food.
Don't repeatedly touch or bite the area.
For pain, a topical oral anaesthetic can be used if appropriate.
Health Tips
A traumatic ulcer should show clear improvement within 1-2 wks after the irritation is removed.if it persists beyond 2 weeks,becomes larger/ harder, repeatedly bleeds or keeps recurring at exactly the same site, it needs an examination by a dentist, oral medicine specialist and possibly further investigation.