You have to refer to the dev branch and reference the SHA of the version of dev you want in Composer.
Example:
composer require drupal/field_group:13.x-dev#COMMITSHA
This will fetch the dev branch of version 8.x-13.x at this specific commit. To get that commit itself, you’ll have to find it on the git page for the project ( which now goes to GitLab).
I can’t find the exact one you are looking for (I’m on mobile) but here is an example.
https://git.drupalcode.org/project/field_group/commit/a4bd38698187c30184d5c76fd884be86e2091fe7
So you’d do:
composer require drupal/field_group:3.x-dev#a4bd3869