Not relevant to your post, but I kept getting asked by data engineers who are interested picking up scala (thanks to spark): how shall I learn scala? Do you happen to have any advice for them?
You could try learning from a book or a course, but personally I've never found a better way of learning "what I need to learn for X" than trying to do X and then googling all the things I don't know.
Sure, you'll forget a whole bunch of that stuff, but if it's at all important you'll find yourself re-learning it again and again until it sticks.