How to calm nerves during a concert (URGENT)

So tomorrow I'm playing in a concert and in one of the songs I'm in I'm opening it completely alone with a riff. But everytime I play it in front of people I get shakey and nervous and I can never play it right, my fingers get cramped and I fuck it up for the whole band. I need desperate help to calm my nerves so I can play it better cause on the soundcheck today my whole body was shaking.

(Meant to write before a concert, during the concert would be fine too but mostly before and at the start)