How would I acess older versions of Doom?

[Puncher_Sponge]

I own all the doom games on steam, and I am wondering how I can get the older versions of doom, like 1.1, 1.2, etc. im stupid idk :/

[kwc]

http://doomgate.de/files/duub/index.html
 

found from:
https://doomwiki.org/wiki/Versions_of_Doom_and_Doom_II