I tried the procedure and had no difficulty following it.
The slight change I wanted to suggest was that some of the text in step 8 should be removed and instead there should be a short introduction saying why you would do the test and what it would achieve. I reached this conclusion before reading this thread where one of the comments is;
The only thing that struck me was that when I first saw it I asked myself, "What do I want to do a loopback test for?"
Suggested text at the start (removing equivalent text in point 8 );
The loopback test will prove that your host computer hardware driver, USB cable, and USB to serial converter are all working.
Try the loopback test after you first install the system or if you cannot upload sketches.