How to access the wirzardstep next to validate a dropdownlist?

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ASP.NET

I am trying to find out how to assess a wizardstep next button (or another way) to require validate a dropdownlist with "select" as the first option.

What I have tried:

<asp:WizardStep runat="server" Title="Personal Information" ID="step2">
                
                <asp:TextBox ID="txtsqlEmail" runat="server" Visible="False"></asp:TextBox>
                <table border="1" width="100%">
                    <colgroup>
                        <col style="width: 60%">
                        <col style="width: 40%">
                    <thead>
                        <tr>
                            <td style="text-align: right">
                            Employee ID:
                        <td>
                            <asp:TextBox ID="txtEmpId" runat="server" Width="200px" AutoPostBack="True" BackColor="#3366FF" Enabled="False" ForeColor="White"></asp:TextBox>
                        </td>
                        </tr>
                        <tr>
                            <td style="text-align: right">Title:</td>
                            <td>
                                    <--!Want to require validate the tile using the next step button-->
                                <asp:DropDownList ID="DDTitle" runat="server" DataTextField="Title" DataSourceID="SqlTitle" AppendDataBoundItems="true"></asp:DropDownList>
                                <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ControlToValidate="DDTitle" ErrorMessage="Please select Title" Font-Size="Small"                                ForeColor="#FF3300"></asp:RequiredFieldValidator>
                            </td>
                        </tr>
                        <tr>
                            <td style="text-align: right">First Name:</td>
                            <td>
                                <asp:TextBox ID="txtFN" runat="server" Width="200px"></asp:TextBox></td>
                            <tr>
                                <td style="text-align: right">Last name:</td>
                                <td>
                                    <asp:TextBox ID="txtLN" runat="server" Width="200px"></asp:TextBox></td>
                            </tr>
                        <tr>
                            <td style="text-align: right">Email:</td>
                            <td>
                                <asp:TextBox ID="txtemail" runat="server" Width="200px" Enabled="False" BackColor="#3366FF" ForeColor="White"></asp:TextBox></td>
                        </tr>
                    </thead>
                </table>
            </asp:WizardStep>