Grade 3 OSMF is a premalignant condition. First you need to completely stop tobacco chewing.
Next Steps
Rinse month with antiseptic mouthwash daily after food
Health Tips
Try to have soft , bland diet with minimum spice. There are oral gels etc available to help to reduce burning. Drunk lot of water, green vegetables, fruits. You can do video consultation with ENT/ DENTIST to show your lesion and have a prescription.