How to control fear/anxiety while speaking? Breathing exercise?

How to control fear/anxiety while speaking? Breathing exercise? What I think about myself is that I can reduce my stammering when I become more calm/normal while speaking to stranger. At this point of time, Whenever I'm in stressful situation e.g, Interview, Senior professional talking to me, my heartbeat increase suddenly and I started stammering more. And I think if I calm during those situation I can speak without much stammering. Has any tried breathing exercise before? Similar to this one 1) https://youtu.be/F6tEygVuy1Y 2) https://youtu.be/7L4Zx3lYIFI exercise start at 0.53 second time.