FusionAuth has a bunch of import scripts, but one that you are probably most interested in is the CSV importer, which takes a CSV file and then calls the user import API.

Here's the link: https://github.com/FusionAuth/fusionauth-import-scripts/tree/main/csv

Of course, LDIF is not CSV.

Instead of using a CSV gem to get the list of users and their attributes, use a gem that can read LDIF. Here's a candidate. https://www.rubydoc.info/gems/ruby-ldap/0.9.19/LDAP%2FLDIF.parse_file but I'm not sure what the state of the art for ruby LDIF parsing is nowadays.

If you pursue this, please submit a PR to that repo because there may be other folks who want to import users from LDIF

An alternative would be to have them manipulate the LDIF file into CSV and import that using the csv importer. See https://www.google.com/search?client=firefox-b-1-d&q=ldif+to+csv for some examples on how to do the LDIF->CSV transformation.