Example:
"id","username","email","firstname","lastname","auth"
567,"rabrown","rabrown@somenet","Aaron","Brown","ldap"
Yes, do remove those users that are set to Admin Moodle from the csv file. No user name, nothing is done.
Yes, do one user ... or use above as a 'ldaptest.csv' file so you can check it out. Create a new 'ldaptest.csv' file in NotePad (NOT a spreadsheet app). Copy and paste the above into that .csv file then use it in your Moodle.
Since you know the user name, search users and see what the authentication is for Aaron.
You've never said how your entity is organized or what it is ... I help public schools in Texas and those that use LDAP are somewhat large, therefore they have OU's per campus - and a couple have separate Moodle instances per campus to absolutely keep students from messing with anything other than their campus stuff.
If you can do this, think setting up a sandbox moodle that is a replication of your production moodle server. One can try out all kinds of things without worry then.
Also, before you start to play with users, **backup your DB** - just in case. And, if you've never done before, research how to restore your DB from SQL (setting up a sandbox instance would give you practice at that).
'spirit of sharing', Ken