“What to say to calm down an angry person?”

Hello! This is a great question. Telling an angry person to calm down, almost never works. First, I think we have to acknowledge that none of us have the power to control other people's emotions. If someone is angry, they are the ones that have to learn to regulate how they feel and what they do when they are upset. So it can be good to remember that it's not your job to help them to be less angry.
If I was responding to someone who was getting angry too often, my approach would depend on the reasons behind the person's anger. Some people are angry because underneath of the anger, another threatening feeling is going on, like fear, anxiety, or sadness. And that other emotion is getting expressed as anger because sometimes it's easier to be angry than sad or scared, for example. In these cases, sometimes some sympathy and listening can help. Saying something like, "I can see that you're angry and I want to understand." That can sometimes help someone move past the anger to what's really going on.
Other times, though, people use anger as a manipulative tool. They've learned that by intimidating others, they are more likely to get what they want. In those cases, a sympathetic, listening ear is not what I'd recommend. Rather, I'd recommend a very firm boundary. Something like, "I don't like it when you speak to me this way, so I'm going to leave. I'm still here for you, but I'll only talk to you when you are more calm." Then it's very important that you do what you say and follow through with your boundary every time. This is very likely to make that person more angry at first, but if you do this consistently, they will get the message that they are not longer able to control you through their anger.

Well the only thing I will suggest is space. Alot of times when a person is angry it's only for that moment as long as it doesn't insue into violence. But if this person has a temper just separate yourself and give them time and space to regroup and come later or a day to discuss whatever was needed. Hope this helps.

Try lowering you voice when she is louder (that will help her mimic your tone) and instead of trying to calm her down do the opposite and hear her anger, feeling heard alone will help calm her anger

Try saying something like, "I understand you are feeling angry. I want to understand what is happening. What is it that you're feeling angry about?" This shows that you are trying to see things from the other person's perspective, which may help him or her feel better. Try to avoid sounding judgmental when you do this.

“Calm down.” “Just relax.” “Don't worry about it.” “Stop stressing out.” “It will be fine.” “Don't get so upset.” We have all probably been told these phrases, or something similar, by another person when we were angry, anxious, or stressed. We may even ourselves be guilty of saying them to another person

See this link...
https://www.wikihow.com/Calm-an-Angry-Person