If you do know the basics, (if you don't, I'd suggest Andrew Huang's video Here ) Id suggest the youtube channel, 8-bit Theory . They do an excellent job teaching valuable theory lessons by analyzing video game music. This might not be what you're looking for but otherwise its a great source for learning.
All theory-links (and most questions and answers of this SE) are giving information and exercises that you can train on any instrument, especially on keyboards. Look up fundamental theory.
I'll post you the very first best link I'll find when looking for music fundamentals