Either harvest the compost (which will be difficult with small worms)or divide the bin into two or more bins, add new bedding and start to feed carefully.
I would loosen up the castings, then cover a layer of the old castings with a layer at least twice as thick of new, loose bedding and let the worms move up in their own time. If they don't seem to be moving, don't worry too much, if there are worms, there are cocoons, and as soon as they hatch they'll move up.
Good Luck

Don't panic, sounds like you still have a good population of worms, they just had to stay small to cope with the conditions. Dividing the bin and adding more bedding and then starting to feed again will likely give you a population boom in a few weeks. Then once the worms seem to be getting up to more normal size, you can harvest some of the old castings out.

Good Luck.

Zone 1 ! Wow!

May I ask 2 dumb questions: When is your last frost? Do you ever put things like basil and tomatoes in your garden?

I agree with the others, your bin could use separating and replenishing, it will most likely be fine. In your place I might take some of the stuff out and spread it around roses or other compost hungry things before your Spring hits. Losing the worms but feeding the flowers. But as you might have a good six weeks(?) before that happens you have time to coax the worms out with new bedding and food and THEN use the compost.

Welcome Home!!
Audrey