When you tell someone who’s nervous to ‘calm down’, you actually make them more nervous.
Because now, on top of already being nervous about at least one thing, they are being told to do an additional thing – right now.
Furthermore, if they are unable to calm down right now (which they are clearly not), then you have given them another task which they cannot complete, and feel more shame about.
No, instead, it’s far better to listen with the intention to understand where they are coming from.
Why aren’t they calm? Would you be if you were them? (You wouldn’t.)
Once they feel that you understand, at least partially, where they are, then you can begin to speak.