Need to see first if only one tooth is discolored or all of your teeth.
If one tooth is affected, history of trauma to that tooth is needed. It can be corrected by root canal treatment followed by capping of that teeth.
If at all, all of your teeth are discolored, history of any habit is necessary, like do you or did you have any tobacco chewing habit. For that, a full mouth scaling followed by bleaching can be done.
Please note that bleaching cannot give you white teeth, it will only give you one or two better shade than your recent tooth shade.
Next Steps
visit a nearby dentist to get the treatment done