Enroll an exising user in another journal OJS 3

I have a question.
We are running a test server with an upgrade from OJS2.4 to OJS3.1
I want to enroll an existing user (which has roles in another journal on the server) into a journal. I can’t find the way to do it!
Under Users and Roles > Users, there is a link “Add user”. When I click there I come to a form to add a NEW user. If I type in the username of an existing user I get an error. How can I find an existing user and add roles to that user?


As a site manager you can add the user to new journals. Go to the journal where you want to add the user and select Users & Roles. Do a search and check the option to “include users with no roles in this journals”. Then edit the found user and add the needed roles.