In addition to deployment of your iOS and Android apps, there is a testing phase where you have to manage your certificates and keystores properly. You have to manage screenshots for your apps, revisions, and much more. In order to do all these things with ease, there is a service called fastlane--a continuous delivery tool for Android and iOS development:
Fastlane brings with it several things: version control, automatic deployment, bringing together iOS and Android apps deployment into one automated process.
This is not something specific to React Native. Fastlane was born out of the need for companies that develop both iOS and Android for ease of common repetitive tasks such as generating screenshots, signing apps, deploying, testing, and so on.
If you go to https://fastlane.tools/ and click on Get Started, you will...