There's a sticky thread on the main page that discusses the step-by-step procedure for a 2.5 PEM, but I know there are significant differences between the 1.5 and 2.5 PEMs.
DIY: Roadster 2.5 PEM cleaning - step by step
This is something that, if you don't know EXACTLY what you're doing, you shouldn't even try.
You get one thing wrong and, if you're lucky, you'll only ruin a multi-thousand-dollar part. If you're unlucky, you'll kill yourself (and maybe your helper friend, too).
Yes, you're correct...Tesla does not publish a service manual, nor do they spell out the steps needed to do this safely. And yes, that sucks. But don't "guess" on this one.