Hi @GoStanford,
The way that I found it easiest to shorten the strap of the Icon was by sticking part of the Tom BIHN ruler against one side of the strap as I fed it down into the hole. Because the ruler has a smooth surface, and a long, flat surface to act as a backing/support for the soft webbing of the shoulder strap, when I grab a section of the strap between webbing and ruler, and push down to slide the strap in to shorten it, the part of the beneath the opening keeps the section of strap that you’re pushing down the side from bunching up near the top of the hole or tangling. Then, once you’ve pushed a section of the strap down, you can slide the ruler up again against the strap, readjust your grip point, and push down the next section.
You want to grip and push down to feed the strap in close to the top of the buckle/retaining mechanism, so I usually have the thumb and forefinger of one hand gripping the strap there to feed it in, and the fingers of my other hand underneath the strap and the flat side of the retaining clip support it — with the supporting hand’s forefinger just under the webbing loop adjacent to the bag. Then, after I feed a section of strap + ruler gripped between thumb and forefinger into the hole, I use my my thumb to rock back and slide the top of the ruler up, so that I can grip the next section of strap and push it into the whole.
It’s similar to the motion that @bartleby showed in his video with the addition of the ruler. Any flat, relatively smooth strip that is not wider than the webbing can be used for this purpose of supporting the soft webbing of the strap as just push it into the hole, and prevent it from bunching up near then opening. I just happened to find the Tom BIHN ruler well suited for this. And, since the ruler was included with the Little Swift, Swift, and Field Journal Notebook — all products that I separately purchased — I had this ready to hand.
HTH
moriond
ETA:
(I think that I actually used this with the ruler on the other side of the locking mechanism, but I don't have a photo of that on my phone, and it's too dark now to take another one. But hopefully, this will give you an idea of what I meant by saying this helps to guide in and support the strap as you feed it into the hole, and that the section of ruler below the opening ensures that there is a flat support for the strap.