Good Morning.
Discolouration and smoking go hand-in-hand. Unless you do not quit, the discolouration will continue , adding to which you could hamper the condition of your gums too. You may seek professional dental treatment at a dental office by getting your teeth cleaned and polished which will provide temperory results but unless you do not quit smoking the yellowish discolouration will keep recurring.
No kind of medicine/ toothpaste/mouthwash will work in such a case.
Next Steps
1. Quit Smoking ( I think this is the best time since the country is facing a lockdown)
2. Get a professional cleanup and tooth bleaching at a dental office ( this will motivate you to refrain from smoking)
Health Tips
1. Maintain a nutritious diet.
2. Rinse your mouth with water thoroughly after every meal.
3. Brush twice/day and floss once daily.
4. Visit a dental office once in 6 months .