Like I used to talk with my boxing mates and school friends and being more confident for more improvement I used to give speech infront of everyone like at initial times I used to stutter a lot but gradually seeing all familiar faces and supporting people I could speech fluently without any stutter it's much more like i didnt give damn about people opinion no matter how much I stutter I would force myself to say that word and I always complete my sentence even if it would take around 5 mins to compete even 50 words. If you wanna know which exercise helped me the most then I would say yoga and meditation for about 10 mins daily and yeah of course boxing too like which made me more confident physically and both mentally, because of yoga I could talk more calmly and focus on present situation like man go outside meet people say them good morning put a smile on your face you gonna cure it , it is simple ,rather than doing around 10 exercises every day just speak with some stranger or your close friends in phone call you gonna see much more improvement