ALWAYS screw the string tensioner button to a wall, by the way. If it's screwed to your window valances (trim) they will BOTH fall apart.

However -

On the buttons that have two strings coming into them, that are knotted together:

If the side the strings come into on the button are against the wall - you can't pull any slack to loop them for adjustment. The string is pinched....

If the string comes in on the side of the button away from the wall - you can't loop slack up and around the button to adjust them.

CATCH 22!

DO THIS instead;

Pull the screw, put a small washer between the wall and the button, and mount it with the string coming in on the wall side. This will create a slight gap so you can pull slack and loop it over...

Go look, and you'll see exactly what I'm saying! This makes adjustment simple.

Lift the shade (ONE SECTION AT A TIME) and pull some slack. Draw it through the button, and then make a half twist before looping it over the button. You can adjust them one half loop at a time this way...