While I agree with everyone that an internship/assistant position will be necessary at some point to learn the workflows and build contacts, having a solid functional knowledge of the basic tools will go a long way to helping you get that internship - I don't really know anyone who would take on an intern/assistant who doesn't have the basics.
You can at least start by getting familiar and fast with all the basics in Pro Tools (assuming that's the platform you'll be working on) - for self-directed, there's tons out there but when I needed to learn Cubase and Logic in a hurry I went to these guys:
https://www.macprovideo.com/library/...ation/ProTools
There's plenty others out there - Berklee probably has some decent online courses. None of this will get you deeply familiar with specific post-pro workflows, but they'll give you some background and get you comfortable with the tools, which is step one.
Best of luck!