What should I do if I have dry cough?

Dry cough. Well, first stop smoking! that should help and if it continues, you need to see your doctor to see if you have damaged your lungs already and need an inhaler. Also, if you are stomach problems, they can make you cough, so really you should see your doctor.
Cough. I see you are a smoker, so the first thing to do is not smoke. As long as there are not other concerning symptoms like high fever, shortness of breath, or blood in mucous then it is likely a simple upper respiratory infection which will resolve within a week or so. If it is due to a bacteria you might need antibiotics. In the meantime you can try a cough syrup for the symptom.
No tobacco. Hydrate well. Consider using a warm air vaporizer. Mix several teaspoons of honey into herbal tea with a squeeze of lemon juice. Or make tea with 2 tsp of marshmallow root bark per 1cup of hot water (steep in a covered pot for at least 5 minutes). Drink several times a day or as needed to relieve coughing. See a physician if your cough is not resolving, difficulty breathing or temp > 104.