How to delete records of checked tasks?

I am making a python todo list application with Flask. I am not aware of how to delete the records of tasks checked in the database. I am using sqlite3.

    {% extends 'base.html' %} {% block heading %} Todo List {% endblock %} {%           block content %}
    <div class="tasks">
    <form action="/deletesel" method="post">
    <input type="submit" value="Delete Selected">
    <br>
    <br> {% for todo in todos %}
    <label class="task">
    <input type="checkbox" class="checkTask">{{ todo.todo }}</label>
    <br> {% endfor %}{% with messages = get_flashed_messages() %} {% if  messages %} {% for message in messages %} {{ message }} {% endfor %} {% endif %}   {% endwith %}
    </form>
    </div>
    <div>
    <form method="post">
    <input type="text" name="newTask">
    <input type="submit" value="Add"> </form>
    </div>{% endblock %}