Since many of us took the rocket course and probably like their own rockets a lot, could you explain how to properly import and export your own assets instead of using the premade ones? Sorry if you did explain and I missed it.
With certain versions of blender you can actually save a copy of the blend file to the assets folder within unity and it will try to convert it over for you. You can work on the file in blender and save changes and watch them update in unity. This does not work with experimental versions of blender and I have not tried it with 2.9 yet but in blender 2.8 it works decent.
There are many things to do when going from one program to another but there are some good resources out there on other courses. The modeling a sword for beat saber livestream from @jlampel walks you through exporting a blend file to unity.
I have not done the rocket course yet so sorry if I am a little off topic.