Mod Custody - Init or Subq Filing?

I am filing a Custody Modification pro se. On the Domestic Civil Action Cover Sheet, would I select Initial Filing or Subsequent ?
I filed a Civil Case for Custody last year and we settled out of court with a Parenting Agreement. I called the Court Clerk asking how much to file the Custody Mod, and she said because I have a previous case filed, there is no filing fee.

This is a subsequent filing. You need to file it under your original file number.