delete button y addButton

I built a website where you can save and delete times. At the beginning I can save. But when I delete, I delete all times and can no longer save anything. Also, when I reload the page, what I deleted is back. Can anybody help me with this? Thanks in advance!

<!DOCTYPE html>
<html lang="de">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Arbeitszeiten App</title>
    <style>
        body {
            display: flex;
            flex-direction: column;
            gap: 16px;
            background-color: white;
            font-family: "Roboto";
        }

         #addbutton {
            background-color: rgb(7, 158, 240);
            color: white;
            border: none;
            font-size: 20px;
            padding: 16px;
            cursor: pointer;
        }

        #deletebutton{
            background-color: red;
            color: white;
            border: none;
            font-size: 20px;
            padding: 16px;
            cursor: pointer;
        }


        input {
            border: 1px solid rgba(0, 0, 0, 0.12);
            height: 50px;
            border-radius: 8px;
            width: calc(100% - 16px);
        }

        .list-item {
            background-color: white;
            border: 1px solid rgba(0, 0, 0, 0.12);
            padding: 16px;
            border-radius: 8px;
            font-weight: 60;
            display: flex;
            align-items: center;
            gap: 16px;
            margin-bottom: 16px;
        }

        .small-img {
            width: 24px;
            height: 24px;
        }
    </style>
</head>

<body>


    <h1>Arbeitszeiten</h1>
    <input id="myDate" placeholder="Datum einfügen" type="date">
    <input id="myStartTime" placeholder="Startzeit einfügen" type="time">
    <input id="myEndTime" placeholder="Endzeit einfügen" type="time">
    <button id="addbutton" onclick="addWorktime()">Speichern</button>
    <button id="deletebutton" onclick="deleteWorktime()" onclick="sicherheitsabfrage()"> Alle Arbeitszeiten löschen</button>


    <div id="myWorkingHours">

    </div>

    <script src="script.js"></script>

</body>

</html>

and the javascript file:



function deleteWorktime() {
    let myWorkingHours = document.getElementById("myWorkingHours");
    myWorkingHours.parentNode.removeChild(myWorkingHours)
}

function sicherheitsabfrage(){
    confirm(message)
}

myWorkingHours.innerHTML = localStorage.getItem('html');

function addWorktime() {

    let currentDate = myDate.value;
    let startTime = myStartTime.value;
    let endTime = myEndTime.value;

    myWorkingHours.innerHTML +=
        `<div class="list-item">
    <img class="small-img" src="img/Uhr.png">
    ${currentDate} ${startTime} - ${endTime} 
    </div>`;

    localStorage.setItem('html', myWorkingHours.innerHTML);
}

I have search 3 hours, but with not results