Just dunk the straps in water and pull them - manually stretched works for me!
I loved their Wahoo ‘indoor trainer bibs’, and the fit perfectly in every way. Then I needed more, and Le Col had the ‘Inspired by race’ new Wahoo indoor trainer bibs. Reviews said they were running ‘small’. order up a size. So hesitantly ordered XL’s. WOW! WAY WAY too small. I asked their customer support what size I should be ordering, and after nearly 2 weeks, they said ‘2XL’. Got them, and the waist was snug, but usable, but the straps were very short! Surprisingly so very short. They leave marks on my shoulders. They otherwise feel great, and the grippers have lasted nearly a year so win, but, yeah: ‘What is it with strap length all of a sudden’? I ordered the XL of their ‘Sport Bibs’, and they fit well, slightly big, but again, the straps are short. I’m 5 10, no giant. What’s up with straps?
Sizing has always been an issue with some brands. 
Now straps?