Here are a few tips that I give to students for performing and dealing with nerves. The third one should be taken very seriously. It's hard to physically get nervous when leaning forward. It's our attach mode. Leaning back is our defense/scared mode.

Play for people beforehand to harden your nerves and to get used to playing under pressure.

Don't start immediately. Take a pause, hear the piece in your head, and take a deep breath first.

Breathe from your stomach and lean forward.

Sing the piece in your head while performing.

Hear the piece as you are playing it as though someone else is playing it and try to enjoy what you are hearing.