In order to Redirect non-www to www on your website, manually edit the web.config file of site and add the following rewrite rule:
<rewrite> <rules> <rule name="Redirect example.com to www" patternSyntax="ECMAScript" stopProcessing="true"> <match url=".*" /> <conditions> <add input="{HTTP_HOST}" pattern="^example.com$" /> </conditions> <action type="Redirect" url="http://www.example.com/{R:0}" /> </rule> </rules> </rewrite>