Hey, the model is triangulated because the STL format is for 3D printing, I think.
So I imported the model into Blender, went into edit mode, selected all the vertices, and used the Alt+J shortcut to turn the triangles into quads.
Now you can import the model using the SubD command in Moi3D and recreate the horns more easily. I’m attaching the obj model.

There are still some triangulated small zones, but is almost quad now





Greetings

Hello Phiro,
Thanks!
“A rebuild” or “reconstructcurve” don't seem to do anything for me. But maybe I'm not selecting the right lines. Or do I need to install a script first? Because otherwise, I'd have to click on every single line segment one by one.

Hi Paf,
Thank you so much for your great dedication and for helping me with this. I'll try Phiro's approach first, and if I get stuck, I'll try yours.