All players can preload Days Gone once they pre-order the game. That being said, to preload the game, all you have to do is find the game in your library and click install. To do this on Steam, you will first need to find the game in your library.
Once you find it, click on the name of the game, and you should see a button labeled preload, click on it, then choose a location to preload the game.
Related: Days Gone: All Nero Checkpoint Locations
On the Epic Games launcher, you will need to click on the game icon in the library section, and after that you will be prompted to choose a location.
Choose a location and the game will begin to download, and once complete you will have successfully preloaded the game on Steam or Epic Games.
When will Days Gone be playable on PC?
Days Gone will be released in full tomorrow around 12:00 p.m. worldwide or 21:00 p.m. PDT. In the UK, the game will be unlocked for players tomorrow at 5am. Days Gone on PC will also include photomode, ultra-wide monitor support, and players can reset the FOV to a maximum setting of 100.
Along with that, the game will also include all of the downloadable content from the console version of the game.
For more on Days Gone, we at PGG have Horde locations in Days Gone and Days Gone: Sarah's Lab Notes Locations