vb.net - How to change Required in an input tag to false -

i have html code , want press button without input data required can redirected previous page, needs in vb.net.

<form runat="server">     <table>         <tr><td>first name:</td><td><input type="text" id="first" runat="server" required/></td>         <td>surname:</td><td><input type="text" id="last" runat="server" required/></td></tr>         <tr><td>date of birth:</td><td><input type="date" id="birth" runat="server" required/></td>         <td>gender:</td><td><select id="gender" runat="server" required><option>male</option><option>female</option></select></td></tr>         <tr><td>known illnesses:</td><td><input type="text" id="illnesses" runat="server" required/></td>         <td>nationality:</td><td><input type="text" id="country" runat="server" required/></td></tr>         <tr><td>email:</td><td><input type="email" id="mail" runat="server" required/></td>         <td>mobile:</td><td><input type="number" id="phone" runat="server" required/></td></tr>         <tr><td>employer:</td><td><input type="text" id="company" runat="server" required/></td>         <td>emergency contact name:</td><td><input type="text" id="emergencyperson" runat="server" required/></td></tr>         <tr><td>emergency contact number:</td><td><input type="number" id="emergencyphone" runat="server" required/></td>         <td><input type="submit" id="btnupdate" value="update" runat="server" /></td>         <td><input type="submit" id="btnback" value="back" runat="server" /></td></tr>         </table>         <p id="parmsg" runat="server"></p>     </form> 

you must delete required attribute. if present, <input> requiring data.