How to use findcontrol ?

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C#

ASP.NET

I have a datalist with images alongwith a button control 'addtocart' within item template.
In order to stop image flickering, I have put this button alone inside update panel.
When I click this 'addtocart' button , I want 'button Checkout' to be enabled true.
This 'Checkout' button is inside footer template of that datalist. The problem is that the 'checkout' button is not getting enabled. Please guide me.

<asp:UpdatePanel ID="dd" runat="server"  >
   <ContentTemplate>
         <asp:Button ID="AddToCart"  runat = "server" Text='Add to Cart'   BackColor="DarkSlateBlue" Width="100px"  Style=" font-family:Arial" ForeColor="White" commandname="myevent">
    </asp:Button>
    </ContentTemplate>
    </asp:UpdatePanel>
    </p>
    </td>
    </tr>
    </table>
    </ItemTemplate>
<FooterStyle  BackColor="AliceBlue"  />
<FooterTemplate>
<br />
    <asp:Button ID="BtnCheckOut"  runat = "server" Text='Checkout'   Enabled="false"
    Width="100px"  onclick="CheckOutBtn_Click" style="z-index: 1; width:80px;cursor:pointer;
    margin-left:350px ; font-family:Arial;  text-align:center; height:22px;  font-weight:600; " > </asp:Button>
<br />

public void dl_item_command(Object sender, DataListCommandEventArgs e)
  {
      if (e.CommandName == "myevent") // check commandname here
      {
          v_FirstSessionTag = "*";
          Session["FirstSessionTag"] = v_FirstSessionTag;
          Button CheckOutBtn = (Button)DataList1.Controls[DataList1.Controls.Count - 1].FindControl("BtnCheckOut");
          CheckOutBtn.Enabled = true;