Steam has a method for organizing games and each of their versions.
Its complicated and I will create a guide that goes into much more detail later that will allow you to get any version you want (some of you may already know what that guides going to be about)
But basically outside of steam servers where you also have to deal with things like depots, manifest, and game IDs you have an easier option called Betas.
Steam allows developers to keep other versions public so that we can use them.
So in short the Beta is just a older version of the game that is public. Not all versions are public so you will have to wait for another guide for advanced users who are willing to get older versions. It was my screwing around that eventually made the devs release these versions. But it was also alot of others too.
But back on track:
The versions that are public these are incredibly easy to access, and heres how:

• First while in your steam library right click BIGFOOT on the left side of your screen.

• Then select properties where you will see different tabs you can access

• Select betas

In that tab is a drop down list of different versions you can play
This only includes one from each major release
(none) - newest
(2019) - 3.0
(2018) - 2.0
(2017) - 1.0




After selecting one and closing out the menu it should begin to install the older version
Multiplayer is still working if you get another player to also change there beta to the same version.

This is a Discord for older versions I made:
https://discord.gg/PRJkZCdWFF

Note: This is not official but anyone who joins it is wonderful! We need all the help we can get to start the community growing for these older versions.