Hi Alexa! I had the same problem, I would always work myself up before a show which would create tension between me and my horse so I found what helped me get past my anxiety it to just pretend nobody is there and drown all outside noise out also I found that talking to people really helps distract me and let out my nervousness. Hope that helps!
Personally I keep calm by breathing and talking to other people around me as by doing this it keeps your mind busy and other people who are not calm you can relate to and then end up calming each other down!
Hope this helps