you can import one user.
In Site Admin, go to Site Users Tab -> Select the option of "Import LDAP Users by Keyword".
A new window will pop up. Type your user name in Find box and click on search.
Once user search is finished, click on username and select import. Import sucessful message will appear.
Now refresh site users tab and then request your user to try and login to QC.
Hope this will resolve your issue.