Well, I took my heart in my hands, or whatever the expression is, anyway, I pulled off the flash/accessory shoe spring, which is what applies pressure to whatever you slide into the shoe, but not with scotch tape as the excel file suggests, because I couldn't get it to work that way, but by gently, gently prying it from the front (lens side) of the shoe, and then pulling it out.
Then I used a jeweller's Philips head screwdriver to undo the four tiny screws, being careful not to let any of them fall into the camera!
That allowed me to pull off the accessory shoe cover. Now, down in the hole on the right side is a larger grey screw and below that a very small and hard to reach silver screw. The silver one is what adjusts infinity for the rangefinder. I'm not saying it was easy: first, to reach the screw (tiny slot head); then, to make a minute adjustment one way or the other, and then look through the viewfinder, see if the image lined up at infinity, then back to the screw again, and so on. I got quite frustrated but finally have arrived at what I think is a pretty good alignment.
Putting the covers back on is very easy, just make sure you carefully press down the front spring clips before sliding the spring cover back in place.
One other thing about my Bessa R3M: the actual rectangle of the rangefinder is somewhat crooked, but I'm not going to get upset about it. If I'd wanted the perfection of a Leica, I would have bought a Leica...or, I would have, if I had the money, which I didn't. The R3M is a darn nice camera and I'm having fun with it.