1. Open the Steam console by putting this into the search bar on your browser : steam://nav/console
2. Put this into the console "download_depot 521890 521895 6155375601379829233"
3. Wait for the version to download, and you can find the downloaded depot in the Steam folder > steamapps > content > app_521890 > depot_521895
4. Double click on the Hello Neighbor application, and now you're playing on the older version.

IMPORTANT: Steam released an update on the 12th Feb 2020, and now it seems that this trick doesn't work. A user has commented some workaround methods on this Steam community guide (https://steamcommunity.com/sharedfiles/filedetails/?id=889624474) but I have not tested any of these methods, so use at your own risk.