I got a used New Nintendo 3Ds Xl with the Happy home Designer Edition. How do I transfer the things from my old 3Ds without loss?

So there's still the old data from the previous owner. If I format the DS or just do a data transfer, I'm afraid that the pre-installed game is also gone.

Do I have to format the DS at all to do a data transfer?

Does anyone have experience with it?

This goes under the data management settings, and I mean that the data on the target system is deleted.