Hi, bud. The Steam key function is a standard itch.io feature. When you buy the game and are taken to the download page the Claim Steam Key button is right there.
Otherwise, at the top of this page should be a Download button that will take you back there, and you can claim your key.
I also believe I see where you bought it yesterday, so I’m going to go ahead and email you an extra key, just in case that you can give to a friend if not needed.
Have fun!
