Telling people to relax while you’re visibly panicking just teaches them that panic is the plan.

Groups read behaviour before words, and when the two disagree they believe the behaviour every time. Your hands, your voice and your pace are giving the real instruction, and no amount of calm language overrides them. Telling people to settle while you are clearly not settled teaches them that words here are decoration. Whatever you are actually doing is the thing they will copy.

If you are rattled, deal with that before you address anybody. Slow your breathing, put the phone down, pick the next single action. Then say something short and let your pace do the reassuring.