You can switch back to the prior version of Hearts of Iron by following the same steps as above, but choosing 1.0.0 in the drop-down menu instead. That should get Steam automatically updating your version of the game. To do so, right-click on Hearts of Iron IV in your Steam library, go to properties, then the betas tab, and select the 1.0.1 beta patch from the drop-down menu.

The recently released Hearts of Iron IV now has a beta version of upcoming patch 1.0.1 available for people to opt-into on Steam.