Stammering is a problem which goes hand in hand with anxiety and stress. Reducing the anxiety and stress and anticipatory thoughts of stammering is the way forward.
Next Steps
Try to practice daily in front of mirror, a small crowd of known people .Try to do yoga and relaxation exercises which can definitely help. Don't shy away from opportunities to speak in the crowd or with people
Health Tips
Avoid smoking and alcohol if any. Avoid too much caffeine and junk food. These can increase your anxiety. Believe in yourself and speak freely. All the best.