Problem with index.htm page

[Joe S.]

I maintain three webs:

web1
web2
web3

Each web has shared borders to that at the top of each page is a title box.
When I link the page in the navigation structure, the name I have given that
page appears in the box at the top of the page.

HOWEVER -- on web1, there is a problem with the index page.

When I look at the files in web1, there is a file named index.htm.

When I look at the navigation structure of web1, there is a "Web1 Home Page"
box at the top of the structure, but, when I double-click on the box --
which normally opens the page so I can edit it -- I get an error -- "There
is no file named index.html in the web."

When I open the file index.htm, the box at the top of the page is not there,
instead, it says something like "To display the name of this page, include
it in the navigation structure."

I want to replace the existing "Web1 Home Page" box in the navigation
structure with the file index.htm. I tried dragging index.htm from the
folders list to the navigation structure and dropping it on top of "Web1
Home Page" -- won't work.

How do I replace the existing Web1 Home Page with my index.htm file?