…Is easy. If your game patched to 1.22, you already have it. This is the exact same code that goes on sale on launch day.
If it doesn’t patch correctly, or you want a fresh install just to be sure, you can re-use your download link right now to get an updated installer.
If you are waiting for Mac & Linux builds, they are now available, and I can trigger a re-send of the links to anyone who wants these, or you can email firstname.lastname@example.org and ask them to re-send your links direct, now that all 3 formats are available.
As I understand it, your steam codes should all activate the minute the game is released which is 16:00 PDT (midnight GMT) On thursday!