how to change port in flask app

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=80)

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

if __name__ == '__main__':
    app.run(host="localhost", port=8000, debug=True)

if __name__ == "__main__":
    app.run(host='127.0.0.1', port=5002)

flask run -h localhost -p 3000