Usually it's a good idea to submit to them a demo reel of your puppetry work. Brief and simple: show them your can perform a puppet, and perhaps sample some voices you can do.
However, they don't come up in the public too often . . . Matt Vogel and Marty Robinson had an open call for one back in 2014, but since then, they seem to have one every (other) year, but they're usually exclusive to those who are already in the business (albeit at the bottom of the totem pole, like Stacy Gordon or Tau Bennett).