If you would like to study simple example how to accomplish that I would suggest to look at Unreal Thumbnail Generator Plugin on GitHub. It is simple tool that loads up asset in 3D viewport and make quick textures/icons from your content. I’m not author of this plugin.
I have made similar editor for my game that was based on Static Mesh Editor. Core principles and implementation is nearly the same. If you want something more simple then Static Mesh Editor might be good starting point.