Install Grav in a subdomain and access it via the root domain

I’m trying to install Grav on a sub domain : subdomain.grav.org
But I want to use it as it was the main domain. So when I type grav . org, i go in fact in subdomain.grav.org
But it’s not working. Where is my mistake ?

On root, I’ve put a .htaccess with:

RewriteEngine On

RewriteCond %{HTTP_HOST} ^grav\.org$ [OR]
RewriteCond %{HTTP_HOST} ^www\.grav\.org$
RewriteCond %{REQUEST_URI} !^/grav1/
RewriteRule ^(.*)$ /grav1/index.php [L]

And on the sub domain (grav1), I’ve put an .htaccess with:

<IfModule mod_rewrite.c>

RewriteEngine On


## Begin - Exploits
# If you experience problems on your site block out the operations listed below
# This attempts to block the most common type of exploit `attempts` to Grav
#
# Block out any script trying to use twig tags in URL.
RewriteCond %{REQUEST_URI} ({{|}}|{%|%}) [OR]
RewriteCond %{QUERY_STRING} ({{|}}|{%25|%25}) [OR]
# Block out any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*\([^)]*\) [OR]
# Block out any script that includes a <script> tag in URL.
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Return 403 Forbidden header and show the content of the root homepage
RewriteRule .* index.php [F]
#
## End - Exploits

## Begin - Index
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index\.php
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
## End - Index

## Begin - Security
# Block all direct access for these folders
RewriteRule ^(\.git|cache|bin|logs|backup|webserver-configs|tests)/(.*) error [F]
# Block access to specific file types for these system folders
RewriteRule ^(system|vendor)/(.*)\.(txt|xml|md|html|json|yaml|yml|php|pl|py|cgi|twig|sh|bat)$ error [F]
# Block access to specific file types for these user folders
RewriteRule ^(user)/(.*)\.(txt|md|json|yaml|yml|php|pl|py|cgi|twig|sh|bat)$ error [F]
# Block all direct access to .md files:
RewriteRule \.md$ error [F]
# Block all direct access to files and folders beginning with a dot
RewriteRule (^|/)\.(?!well-known) - [F]
# Block access to specific files in the root folder
RewriteRule ^(LICENSE\.txt|composer\.lock|composer\.json|\.htaccess)$ error [F]
## End - Security

</IfModule>

# Begin - Prevent Browsing and Set Default Resources
Options -Indexes
DirectoryIndex index.php index.html index.htm
# End - Prevent Browsing and Set Default Resources

More simple: my provider has the option to point the main domain to the sub domain