I've been searching for a while now trying to find out docs on how to set up Facebook pixel with an existing react native app is there is package that does that or anyone with experience doing that can help me.
According to Facebook Pixel's docs, Pixel is available only on websites. To track events in mobile apps, you could use App Events.
Regarding React Native, Facebook ended its official support for their wrapper, but you can use the community maintained react-native-fbsdk-next library, as also suggested by Facebook itself. Specifically, to track analytics events, you can use the AppEventsLogger.