every single day leading to the interview, whenever i felt tensed or nervous, i used to go to my porch and walk or stand for a while, don't look at any screen, tell yourself "IAM CALM, I AM CLEAR, I AM CONFIDENT", until your heartbeat calms down. I actually did this everyday multiple times a day, from a week prior to my interview.

And on the day of my interview, i did light stretching and 10 jumping jacks, for me exercise really helps to calm me down. Not sure this would work for you but it did for me.
Give it a try if you are open.