If you are playing on PC and have not yet linked your Steam account to a PlayStation Network account, the game will prompt you to do so when you first launch it. The game will display a QR code and a link to a log-in page for Sony’s PlayStation Network.
If you already have a PSN account but are not currently logged into it on your PC, follow the provided link or use the QR code. Then, use your credentials to log in and link your accounts.
If you do not currently have a PSN account, first follow the provided link or use the QR code, then follow the instructions to create a PSN account. If you followed the link on your PC, this new account should be automatically linked to the Steam account you used to purchase the game. If not, follow the link or QR code again to log into your new PSN account, and link the accounts.
Should you find yourself having trouble creating or logging into a PSN account, please contact the support team over at Sony: https://www.playstation.com/sv-se/support/account/