I bit the bullet last week and paid $18 for this udemy course on 3D printing design for dummies using the free s/w fusion 360. I'm halfway through and its good. I saw today that it has dropped $4. Better than nothing so not a bad time to learn some new skills.
https://www.udemy.com/designing-for-3d-printing-with-fusion-…
Somebody who actually paid for and studies an Udemy course! You deserve an award.