Roundcube access from webmail.domain.com

I have roundcube installed in one of my domains. but users need to type domain.com/roundcube to access it. What should I do in order to get it working with webmail.domain.com??

Also, I read that you can have it redirected for all your domains, but that is not the case… I need a separated roundcube for some domains, so does the redirect…