How to redirect from blog.example.org to example.com using htaccess

I've tried every way to make a 301 redirect since blog.example.org at https://www.example.com/post using .htaccess but the redirection does not seem to work.

I'm using this code below;

RewriteEngine On
RewriteRule ^ blog /(.*)$ https://www.example.com/post$1 [L,R=301]

Please share with me what I could do wrong.