WWE 2K19 has many new unlockables when it comes to all of the superstars, arenas and championships. You can unlock them easily by using the Accelerator, as part of the WWE 2K19 Deluxe Edition, WWE 2K19 Season Pass, or as a separate WWE 2K19 DLC, that is purchasable from the Playstation or Xbox Store, and is cheaply priced. The use of the accelerator in WWE 2K19 will unlock everything, this includes all of WWE 2K19’s unlockable superstars, arenas, championships, as well as all of the Daniel Bryan 2K Showcase mode unlockable.
If you do have accelerator pack, you will see Unlock everything button (square or X depending on your platform) / option on purchasables section.
Note: If you not seeing square or X. Go back to your download items and reinstall it. A simple restart of the game may work.