Add an event listener to the first button that changes the text within the to EITHER uppercase or all lowercase

Hello code friends I have an assignment, new to this

Add an event listener to the first button that changes the text within the to EITHER all uppercase or all lowercase, depending on current state.

I need to change all paragraph under h1 to lowercase or uppercase, at the click of a button.

in HTML
I made an id to p.

I made a button with an id

in JS
I used getElementById to bring my button and paragraph.

const textChange = document.getElementById(“btnChange1”);
console.log(textChange);

const txtChange = document.getElementById(“myP”);

textChange.addEventListener(“click”, () => {

}
});

that’s as far as I can get, thanks in advance!