To unlock your pre-order bonus items in Dragon’s Dogma 2, the ring of assurance and the superior weapon quartet, you’ll have to earn them in-game.

Go through the opening couple of steps of the first quest, Tale’s Beginning.
Specifically, during the third step, you have to make for Melve right after interacting with the first riftstone.
Before you go to Melve, head into the nearby blue tent that has a picture of a hearth in front of it.
This is the borderwatch lounge. The innkeeper will let you sleep for free, so use that opportunity.
After you rest, talk to the innkeeper again, you should get a message telling you that you can collect your items at any inn by talking with the keep.

You don’t have to do this right now if you don’t want to.
You can choose to pick up your bonuses later on at any inn.