Where can I download an old version of the Hueman theme ?
You can download a previous versions of the Hueman theme in two places : WordPress and Github.
Visit the releases page, and download the .zip file.
For example, if you need to download v3.1.0, use this link : https://downloads.wordpress.org/theme/hueman.3.1.0.zip.
You can change the version number (3.1.0 in the example) by the one you need.
If you don't know which version you want, the version history is available here : https://wordpress.org/themes/hueman