Creating a new Nintendo network ID on 3DS with games on it

So I got this used 3DS XL at a pawn shop that has a number of different games downloaded on it. They told me when I bought it that the games were tied to the system so not to try to reset it myself or I would lose all the games and the save data.

I recently went to the Nintendo eShop and wanted to download the Pokemon Sun and Moon Demo. When I went to do so it said I needed to link a Nintendo Network ID in order to use this software and prompted me to go to the NNID settings.

When I went to the System Settings and then to the NNID Settings, it said “Hi there, kids! Please have a parent or guardian look at this for you, OK?” then when I hit A (OK) the next screen said “Welcome! You can link a Nintendo Network ID to your system here.” The next few screens have info about the NNID and then I reached a screen that had two options; one to link an existing ID and one to create a new ID.

I am assuming that this means that there is not a NNID linked on this 3DS. So what I was wondering is: first off if someone could help me confirm if my assumption is correct or not; and two, if I proceed and create a new NNID on this system, will I lose the games and save data I already have on it?