Yeah, you take a digimon that can get sick from the cold. Let it get sick, keep walking around Freezeland and eventually it will trigger something and you'll end up in Frigimon's. Then go do something else and get a digimon that does NOT get sick from the cold, then talk again to Frigimon and you'll recruit it.
The digimons that can get sick from the cold are all Babies, In-Training, Agumon, buy moldy meat from vending machine in ancient dino region.
it always make digimon sick if you feed them with it