how to create another svn user

This is a "duh" kind of post, but given that you haven't created a new svn user in several months, you can forget!
 
Use the "htpasswd" command that is in your path.
The private-svn-auth-file is a file that you use to store the SVN users and is how you configured your apache server
htpasswd /etc/private-svn-auth-file <username>