Import your Obj file into the list on the left. wait for it to refresh (or click the flag), and then copy the string that generated below. Once you have the string below, copy it. In glue3D, press the "page up" button to show the engine files. find the model that you want to import the Obj into, and replace the data under the "model" header with the string you copied. Make sure you're not editing the model too, or you'll overwrite the Obj with the empty loaded model. that's it!
Yea so it's literally just dark mode ig, kinda useless until Glue3D actually comes out.