mine had a little pamphlet or card in it that hat a code on the back. You then go into the playstation store and top right beside the cart icon it says more I think or something like that, I dunno the icon beside the cart anyways lol. if you click on that there is a redeem code option. Type in the code and it will say successful and download the ps5 version.
on your dashboard if you click on the game it will open a bigger picture of the game and there is a spot with 3 dots. if you click on it you can switch between the ps5 and ps4 versions