Surfece Registration: superimposition of two model - SlicerCMF

Hi, I have a problem and I need help. I need to superimpose a 3d model (an stl file imported as segmentation) to a CT segmentation and I would like to use the SlicerCMF plug-in. The problem is that when I select the module Surfece Registration when I try to select the fixed model and the moving model nether the stl model and the TC segmentation appears in the drop down menu.
How can I solve this problem? Than you in advance!

[Schermata 2021-03-01 alle 17.33.17|690x431](upload://m8