Dragon Ball FighterZ Limited Edition Code not working

I just recently bought Dragon Ball FighterZ for the Nintendo Switch. It comes with two codes for the SSGSS Goku and Vegeta and Super Butoden game.

But upon entering the code on the eshop, it prompts an error "The product associated with that code is not currently available".

I just realized that the game I have bought is the asian/Japan version and my account is set to US.

Is there a way or a workaround that I can do to use the code but still using my US Nintendo Account?

No, unfortunately DLC is always region-specific. This is true for all recent consoles, not just Nintendo.

For a PlayStation account, it's possible to create a new account for the DLC's region, after which you can then install and download the DLC. After that, you can switch back to your original account, and play the game (which is region-free) with the downloaded DLC.

However, I don't think this can work for Nintendo consoles, since they are always linked to a single Nintendo account (for as far as I know, at least). Therefore, it looks like are unfortunately out of luck, and cannot access the DLC with your current account/console.