There is one arrow button besides the button you clicked on. See my attachment. You need to click on that arrow and then need to select "Import LDAP Users By keyword".
If this option is not present in QC 9.2, then there is one more workaround. In the screen shot you shown, user name will be presented inside one of the three usernames shown (eu1, schema, configuration). you need to click on '+' sign and then need to seach manualy for username.
OR
if you know how to set Filter (object class=*), then you can apply the filter for user here also and can search him. It will be like ou=external. o=sca etc (this can be seen from domain authentication which is shown for each user in Site Users Tab).
Kindly proceed and let me know how it goes.