This was already done. The file index.htm exists, and it is first in the list at the IIS site level Default Document. It is also correctly configured in the web.config file for the IIS site. IIS and the server have been restarted (several times) since those changes.
<defaultDocument>
<files>
<clear />
<add value="index.htm" />
<add value="index.cfm" />
<add value="Default.htm" />
<add value="Default.asp" />
<add value="index.html" />
<add value="iisstart.htm" />
<add value="default.aspx" />
</files>
</defaultDocument>