Q.How To Ripen Acorn Squash?
I had to pick my acorn squash because I noticed that an animal had gnawed a bit out of a couple of them. They are dark green and firm, came of the stem easily, and the vine was beginning to wilt. We have had squirrel and chipmunk problems this summer as it has been very dry and I think they eat anything for liquid they can find.

Certified GKH Gardening Expert
Acorn squash, or any harder squash for that matter, will not ripen all of the way once picked. It will mature just a little more, but it will not ripen like summer squash will.
In any sense, you can make the best out of it by following the same practices for ripening summer squash. this article will help:
https://www.gardeningknowhow.com/edible/vegetables/squash/ripening-green-unripe-squash.htm