ASP.NET Clear CheckBox List in Function

I am trying to implement a Clear All Checkboxes upon a checkbox toggle.

<div class="form-group" id="divSelectDay" >
    <label class="control-label col-md-2" id="lblSelectDay">Select Day of Week</label>
    <div class="col-md-3">
        <div class="input-group">
            <asp:CheckBoxList ID="chkSelectDay" CssClass="chkLabel" ClientIDMode="Static" runat="server" AutoPostBack="false" CellPadding="5" CellSpacing="5" RepeatDirection="Horizontal" RepeatLayout="Table"> 
                <asp:ListItem Value="Monday">Mon</asp:ListItem>
                <asp:ListItem Value="Tuesday">Tue</asp:ListItem>
                <asp:ListItem Value="Wednesday">Wed</asp:ListItem>
                <asp:ListItem Value="Thursday">Thu</asp:ListItem>
                <asp:ListItem Value="Friday">Fri</asp:ListItem>
                <asp:ListItem Value="Saturday">Sat</asp:ListItem>
                <asp:ListItem Value="Sunday">Sun</asp:ListItem>
            </asp:CheckBoxList>
        </div>
    </div>
    <label class="control-label col-md-2"></label>
</div>  

On the same page, I have an existing toggle function, which shows/hide the checkbox list whenever "Daily" checkbox is checked or not. But it does not clear them.

function ToggleExecutionSchedule(controlId) {
    var frmControl = document.getElementById(controlId.id);
    var divDay = document.getElementById("divSelectDay");

    var checkbox = frmControl.getElementsByTagName("input");
    var counter = 0;
    for (var i = 0; i < checkbox.length; i++) {
        if (checkbox[i].checked)
        {
            if (checkbox[i].value == "Weekly")
                divDay.style.display = 'block';
        }
        else
        {
            if (checkbox[i].value == "Weekly") {
                divDay.style.display = 'none';
                //clear divDay/chkSelectDay checkboxlist <===
            }
        }
    }
}

I saw some articles on using CheckBoxList1.Items.Clear();, but I am unable to retrieve the value of my checkboxlist chkSelectDay inside my function.

Thank you.