My HTML

Thanks for your help!

My HTML (focus on drop down list)

Thanks for your help!

EDIT BELOW

Following question about "Where in the HTML is an element with name="submit_button"?" I edit adding the full code.

There is an other submit_button which enables me to post a new task. I am then displaying a table with all the tasks and I want to be able to update the status of the tasks, but I can't manage to get the new status to update my database and then update the display of the to do list.

My full HTML

    <form action="/" method="post">
        <div class="form-group">
            <input autocomplete="off" autofocus class="form-control" name="newtodo" placeholder="Type a task" type="text" required/>
        </div>
        <button class="btn btn-primary" name="submit_button" type="submit" value="add_task">Add</button>
    </form>

    <table class="table table-striped">
        <thead>
            <tr>
                <th>#</th>
                <th>Task</th>
                <th>Status</th>
                <th>Action</th>
                <!--<th>Save</th>-->
            </tr>
        </thead>

        <tbody>
            {% for task in tasks %}
                <tr>

                  <td>{{ task.id }}</td>
                  <td>{{ task.todotask }}</td>
                  <td>{{ task.status}}</td>
                  <td><select name= "task_action" method="POST" action="/">
                      {% for action in actions %}
                      <option value="{{action}}" selected='selected'>{{action}}</option>
                      {% endfor %}
                      </select>
                  </td>
                  <td><form action="/" method="post">
                          <button class="btn btn-primary" name="submit_button" type="submit" value= "{{ task.id }}">Update</button>
                       </form>
                  </td>
                </tr>
            {% endfor %}
        </tbody>
    </table>

My full app py

@app.route("/", methods=["GET", "POST"])
@login_required
def index():
    """Show to do list"""

    if request.method == "POST":
        # Ensure it is the button for adding task
        if request.form['submit_button']=='add_task':
            # Ensure added task is not empty
            if not request.form.get("newtodo"):
                return apology("must key a task", 400)
            new_todo=db.execute("INSERT INTO todolist(userid, todotask, status, date) VALUES(:userid, :task, :status, :date)",
                          userid=session["user_id"],
                          task=request.form.get("newtodo"),
                          status="new",
                          date=datetime.now())
            flash("Added!")
        else:
            flash("Hold on!")
            db.execute("UPDATE todolist SET status = :status WHERE id = :task_id",
            task_id=request.form['submit_button'],
            status=request.form.get('task_action'))

    tasks = db.execute("SELECT * FROM todolist WHERE userid = :user_id ", user_id=session["user_id"])

    for task in tasks:
        tasks=tasks

    actions = ['On hold', 'Completed', 'In progress']

    return render_template("todolist.html", tasks=tasks, actions=actions)