Test new wordpress site when old html one is live

Hi,
I am trying to convert my old html site to a WordPress site.
To make it I installed WordPress and also some themes on the root directory.

The problem is that the site must remain live together until is not all ok.

the old one point on index.htm, the WP one to index.php.

If I setup a WP Themes and I don’t add a rule to .htaccess it goes always on index.php.

If I set on .htaccess this rule :
DirectoryIndex index.htm index.php index.html
I access to old site index.htm but index.php is inaccessible also when I point directly to https://www.mysite.com/index.php

I have tried also this rules, to permit my ip address to go on index.php, and others to index.htm, but it doen’t workes (where 000 are subst with my ip address):

SetEnvIf HTTP:X-FORWARDED-FOR ^000\.000\.000\.000$ owner
<IfDefine owner>
DirectoryIndex index.php
</IfDefine>
<IfDefine !owner>
DirectoryIndex index.htm
</IfDefine>

Also this :

SetEnvIf Remote_Addr ^000\.000\.000\.000$ owner
<IfDefine owner>
DirectoryIndex index.php
</IfDefine>
<IfDefine !owner>
DirectoryIndex index.htm
</IfDefine>

If I rename index.php to indexa.php I have the two site but when I try to use WP I always get redirected to htm homepage.