If you are running omnibus package and want to access database directly you have to do these steps:

su - gitlab-psql

for versions older than 7

/opt/gitlab/embedded/bin/psql gitlabhq_production

for newer:

/opt/gitlab/embedded/bin/psql -h /var/opt/gitlab/postgresql -d gitlabhq_production

now you have running psql console.

If you move user to different organizational unit user will not be able to log into the GitLab anymore and you have to change its DN manually. This information is stored in table identities. For example:

UPDATE identities SET extern_uid = REPLACE(extern_uid,'OU=Users','OU=IT,OU=Users') WHERE id = 9;