Moving Nintendo eShop games from a 3DS to a New 3DS

I bought a Nintendo 3DS the week it came out. Loved it, but it failed to recognize my 64GB microSD card for external purchases. (Not a problem, expect that I realized "hey, if I buy Hyrule Warriors, Smash Bros, etc. via virtual download I won't have to bother carrying extra cartridges!")

Since the system wouldn't recognize my "external" games, I bought a used New Nintendo 3DS XL off of OfferUp. Now I'm trying to figure out how to transfer my existing digital purchases (I already paid retail for Smash Bros 3DS and Hyrule Warriors 3DS) to my New 3DS.

I thought this would be a Nintendo eShop ""login and download your games", but I'm having trouble. I searched the Nintendo help three times (and Google/StackExchange each twice) without result.

My question, fundamentally is: *how do I log in to my old 3DS/Nintendo account (or otherwise transfer digital downloads to my New 3DS) to my (previously owned) New 3DS so I can (finally) play the games I paid for 18-36 months ago?

Last I checked, 3DS games are tied to the system you purchased them on rather than just the account. However, it is possibly to permanently transfer them to a new system using the 3DS System Transfer feature.

Nintendo also has a video on how to do it: