I believe there are relatively few magnetic 6x6s out there (it's probably the second hardest WCA puzzle to magnetize, after a megaminx. I've never tried a Square-1, though.), there probably aren't any tutorials. I've made 2 magnetic 6x6s, but I'm not in the video business. Basically just look up a tutorial for a magnetic 4x4, and once you magnetize the inner layer the same way the outer 2 layers are the same as magnetizing a 5x5.