Rocket League account items transfer?

So I used to have a ps4 account with a lot of items in rocketleague, now I've got it on my PC and logged in with psn but still don't have the items, the epic name is shown to me and not my ps4 name, that's normal and how do I get my items?

You have to link the accounts:

https://www.rocketleague.com/activate/

The items you have unlocked on one account are then also available on the other linked ones.