>>53526724To add funds to buy eshop titles. I want Gold on my second 3DS to act as a relay to transfer Pokemon between titles on my primary 3DS. You can't add funds to the 3DS eshop anymore, so to buy titles you need to merge the 3DS eshop with a NNID account, then add funds via the website or the Switch eshop. It's a pain in the ass but it does work.
>>53526735Bank needs to detect a game that it can work with, meaning you need a game that's progressed far enough to get a Pokedex so the Poke Transporter can use it. BW/BW2, any of the virtual console games, XY, ORAS, or SM/USUM qualify for that. If you have a virtual console title just boot up a new save and speed to get the Pokedex. Then Bank will detect it and show you the menu, which lets you download the Poke Transporter.