as-app/docs/create app icon.md

easy free online service

https://easyappicon.com/

old method

In android sutodio, right click on android/app/src/main/res -> New -> Image Asset -> type: Launcher icon, name: ic_launcher

AND / OR

npm install -g yo generator-rn-toolbox
yo rn-toolbox:assets --icon <path to your icon>