Hi, redness can be appreciated in that pic, this might be an allergic reaction. When did you observe this? Have you placed something on that cheek for a long time? Have you tried anything new or have changed your toothpaste? Is it painful?
Next Steps
If it is not painful/ if it is an allergic reaction it will get cured by itself. If it is painful then apply mucopain gel on that particular area. Rule out the possible causes for that and avoid using them.
Health Tips
No need to worry it will be cured within a week. But if is the same or increasing day by day then you must visit the dentist.