Importing Custom Fields

Hello,
Sorry to bother, but I wanted to try and add custom fields (added to user profiles with a different plugin) to the user import process. I looked at some of the other forum posts on similar topics, but wasn’t sure what specifically I might do to get this to work. I also tried to find the documentation, but failed (I’m probably just overlooking it somehow).

Sorry for the trouble, and thanks,
Youki Iimori