It’s pretty easy
Club Nintendo was pretty much the best.
You’d pop open that new game case, and other than the new game smell, you’d get a cool little Club Nintendo insert to redeem for points. Since then the My Nintendo reward system has been a huge step down, but it exists, and there’s now a way to redeem physical copies of games on the Switch (RIP Wii U).
All you have to do is pop open the case in the same way, glare at the lack of instruction manuals and inserts, put the cartridge into your Switch, then press the “+” button on the homescreen to bring up its menu, and select “My Nintendo Rewards program.” From there you can redeem it for Gold Points. Any user on the system can get the reward, you just select them at the point of redemption.
Make sure you do it sooner than later as there seems to be a one-year limit on some games. It’s easy enough where it shouldn’t be an issue! As a note, I earned 12 Gold Points for Zelda: Breath of the Wild.
My Nintendo [Nintendo]