SVN users and their hashed (encrypted) passwords is stored in a file on your server. The name of the file could be dav_svn.passwd for example.
In order to add more SVN users to this file so that they can login to the repositories, you need to execute HTPASSWD command on this file with the username as a parameter. Here is an example:
htpasswd -s /home/mysite/dav_svn.passwd myuser
In the command above, we’re executing HTPASSWD with parameter -s to specify SHA hashing for the password, then the path to the SVN users file (dav_svn.passwd) followed by the username.
The username can be a non-existent user to create a user or it can be an existing user to modify the existing password.