If you do not have the file already - create one in the root folder of the site called web.config
Edit this file and paste the following:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<rewrite>
<rules>
<rule name="WordPress Rule" stopProcessing="true">
<match url=".*" />
<conditions>
<add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
<add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" />
</conditions>
<action type="Rewrite" url="index.php" />
</rule>
</rules>
</rewrite>
</system.webServer>
</configuration>
Save and Retry.
