Native splash
Content
Native splash at this moment shows the most common pattern for this kind of screens:
It shows a logo in the middle of the screen with theme background on iOS and gradient on Android.
Changing logos
To change the logo you have to do the following:
iOS
- Create your icons with appropriate sizes (1x, 2x, 3x)
 - Replace them in 
ios/YourProjectName/images.xcassetswith the same name (splash.png) - Check the result in XCode by opening 
LaunchScreen 
Android
- Create your icon with appropriate size (xxhdpi)
 - Replace it in 
android/app/src/main/res/drawable-xxhdpiwith the same name (splash.png) - Your gradient and splash files are located in 
android/app/src/main/res/drawable, you can also change them if needed 
Tip
Don't use text on your logos on both platforms, try to place just logos.