I’m following how to do this on line but I can’t seem to get the 6th E string to go through the roller hole twice, as instructed. It just seems impossibly thick to achieve this.
Can't think why any string needs to go through the hole twice!
Difficult to describe in words, but here goes.
Put one end of a string through the hole in the bridge, pushing away from the soundhole. Pull 3-4" through. take that end over the bridge, round the long part of the string, and wrap it round itself a couple of times.
One more wind takes the end over the edge of the bridge, towards the body of the guitar. By pulling the long part of the string, it'll all tighten up leaving the simple task of putting that end into the machine head hole, and turning the knob the right way giving three or four complete turns to tighten the string roughly to tension.
Then the time consuming job of tighten, tune, stretch, tighten, tune, stretch, tighten, tune...
If, however, you mean the hole at the tuner end, forget it. There's no need to put any string through twice! And if yo mean the fat E, certainly forget it. Also forget it with the thin E. Just because something is on the internet doesn't mean it's good, authentic, sensible, feasible, workable, etc., etc.!
It's not essential that you go through the tuning roller twice - that's just a general instruction, and the gauge of your string might prevent you from doing it.
The purpose is to increase the friction so the string doesn't slip. If you can't go through twice, go once with enough of a 'tail' to place under the next wrap or two of strings - then the string tension will keep it from slipping.