Hey there @SvenGG! Welcome back to the community! If it’s still available, it should be accessible in your creator portal. I believe it had to be within 2 months of the release of the signups according to this news article:
https://create.fortnite.com/news/fortnite-ecosystem-gdc-2024?team=personal
Though I cannot find information on when the codes originally went out so I cannot verify exactly when the event ended.