This will help you:
I took it from internet because they explain it more easily as I would do
Here's a step-by-step guide on how to perform pursed-lip breathing:
Relax your neck and shoulder muscles: Sit or stand with good posture.
Inhale slowly through your nose: Count to two while inhaling, feeling your belly expand.
Purse your lips: Pucker your lips as if you were going to whistle or blow out a candle.
Exhale slowly through pursed lips: Count to four or longer while exhaling, making the exhalation longer than the inhalation.
Repeat: Continue this cycle for several minutes, or until your breathing returns to normal.