If it is the last tooth ie the wisdom tooth, then it has to be removed if there is no sufficient space in there. A picture and an xray will help understanding if it can be kept. If it is some other tooth, then it might be infected. An xray again is required to see the extent of the caries if present . If shallow, filling will help, if deep, rct has to be done.
Next Steps
A direct or video consultation.
Health Tips
Consult ASAP.