redirect subdomain page to a domain page in wordpress multisite

Hello

I need to redirect one subdomain page to a domain page like this:

https://subdomain.domain.com/register/ to https://domain.com/register/

How can I do this in .htaccess?

I want to redirect only one page from the subdomain to one specific page in the domain. I really need a help with something similar to:
RewriteCond %{HTTP_HOST} ^sub\.domain1\.com$ [NC]
RewriteRule ^(.*)$ https://www.domain2.com/$1 [QSA,R=301,L]

But I am not sure how to do it on page level. I appreciate your help.

Please note that I don’t want to transfer the whole subdomain to the domain, What I want is only one page redirection.