Every part of God's word can help us with this, somehow.
I think I'll offer 1 Samuel chapter 30.
David, before he became king of Israel was trying to stay away from Saul who was trying to kill David. Then, one time, David and his men went on a military maneuver, and the Amalekites raided their city Ziklag and took their wives and children.
First, they did the uncalm things. The wept until they could weep no more; yet, they somehow had the energy to talk about stoning David. May be he had been wrong . . . to lead his men on a military escapade, instead of making sure their families were safe. But crying and blaming did not work.
What worked was how David got encouraged with God, then consulted with God about what to do. Instead of uncalmly questioning God or assuming what he should do, David made sure with God.
And I understand he did what God encouraged him to do. And he would be wise to be calm to realize he could have helped that disaster to happen.
Then they beat the living daylights out of the Amalekites and got all their wives and children back. But certain rotten scoundrels in David's army then insisted that only the fighters should get plunder from the defeat of the Amalekites. The guys too weak to fight had watched the supplies; the scoundrels said no way should those weak guys get anything but their own wives and children.
But David was about family. So, he refused to go along with that anti-family, anti-sharing stuff. Part of his being calm, then, was he handled things as family.
We can lose our calm, I see from this, as we get focused on how things are on us and what we ourselves are able to do. Instead we need to submit to God and discover how He encourages us, satisfies us, and guides us. Do not trust less. Do not trust how worry would hurry us to draw conclusions, lying about what will be or could be or might have been. Do not trust how anger and unforgiveness might drive us. Do not give in to how stress and haste and ambition will waste us. Do not trust those dominating and dictatorial drives and feelings which can be so overpowering and convincing, but they are the pathological liar. Instead, personally share with our Father in His peace, and discover how our Creator creatively guides us to love each and every person.
"And let the peace of God rule in your hearts, to which also you were called in one body; and be thankful." (Colossians 3:15)
We can lose our calm as we take things on ourselves, and even get isolated so we feel on our own. We can pray with each other, share with each other, but be ready to evaluate who we are wise to share with. And be ready to detect and forgive anyone who fails us > have
"longsuffering" ready > Ephesians 4:2 < so we don't become an emotional basket case when people turn out to not know how to love. But then be their good example to help them.
This is possible with God, of course
So, we feed ourselves to be calm, by depending on God, knowing He is able to do all that is really good with us, and be ready for family sharing and forgiveness.