https://www.theverge.com/2018/11/16/18096864/pokemon-lets-go-pokemon-go-transfer-switch-iphone-android

One of the most interesting aspects of Pokémon: Let’s Go, which launches today on the Nintendo Switch, is that it connects with the mobile game Pokémon Go. All of those creatures you’ve been capturing on your phone? You can now bring them to the console game. Well, some of them, at least. Luckily it’s a fairly painless process to sync the two games, but there are a few hitches to be aware of. Here’s how to get going.

The first step is to sync your devices. For the Switch, all you need to do is go to the main menu in Let’s Go and choose “Open Pokémon Go settings.” Once you do that the game will start searching for your Pokémon Go account. While that’s happening, open Pokémon Go and go to the settings menu. (First tap the big poké ball in the center of the screen, and then “settings” in the top right corner.) If you scroll all the way down to the bottom, there will be a list of devices, with the Nintendo Switch at the very top. Tap “connect to Nintendo Switch” and you’ll get a notification on the Switch that a Pokémon Go account has been found. Choose “yes” to sync and you’re all done.