How to redirect to a subdomain using htaccess?

Question

Yii

Moved to another hosting. There, both the domain and the subdomain will be erased into one folder. You need to do the following using htaccess:
all requests to mysite.com go through index.php
all requests to admin.mysite.com go through admin/index.php I
am almost not familiar with htaccess, I wrote this myself (does not work):

RewriteEngine on

# hide files and folders
RedirectMatch 404 /\.git
RedirectMatch 404 /composer\.
RedirectMatch 404 /.bowerrc

RewriteCond %{HTTP_HOST} ^nationsorg\.eu$
RewriteCond %{REQUEST_URI} !^/
RewriteRule . index.php

RewriteCond %{HTTP_HOST} ^admin\.nationsorg\.eu$
RewriteCond %{REQUEST_URI} !^/admin/
RewriteRule (.*) /admin/index.php

in the admin folder like this (in fact, it was similar at the root before):

RewriteEngine on

# hide files and folders
RedirectMatch 404 /\.git
RedirectMatch 404 /composer\.
RedirectMatch 404 /.bowerrc

# If a directory or a file exists, use the request directly
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Otherwise forward the request to index.php
RewriteRule . index.php

Answer 1

If I understand the problem correctly, then:

RewriteEngine on

# hide files and folders
RedirectMatch 404 /\.git
RedirectMatch 404 /composer\.
RedirectMatch 404 /.bowerrc

# Redirect to admin
RewriteCond %{HTTP_HOST} ^admin\.nationsorg\.eu$
RewriteRule ^(.*)$ admin/$1 [L]	

# If a directory or a file exists, use the request directly
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Otherwise forward the request to index.php
RewriteRule . index.php