Uhhh ... LDAP is normally set up in Moodle where change to a profile login/username, etc. in Moodle is not allowed ... fields are locked ... data can only come from LDAP.
So, in this case, me thinks you will have to directly manipulate the DB for that user. Got PHPMyAdmin installed ... use that ... mdl_user table.
Don't have PHPMyAdmin ... then study up on mysql cli client and how to locate a record as well as change data in columns.
'SoS', Ken