I took a stab at doing this myself. I added an email address and password to the LDAP user using the tools described at https://wikitech.wikimedia.org/wiki/LDAP , tested logging in as "simetrical" to wikitech.wikimedia.org, and then sent a password reminder email. You should have received a temporary password which you can use to log in and set a new password for the account. Then you should be able to log in to the Gerrit web interface and set up SSH keys using https://gerrit.wikimedia.org/r/#/settings/ssh-keys