Go to your React native Project > Android
Create a file local.properties
Open the file
paste your Android SDK path like below

in Windows sdk.dir = C:\\Users\\USERNAME\\AppData\\Local\\Android\\sdk
in macOS sdk.dir = /Users/USERNAME/Library/Android/sdk
in linux sdk.dir = /home/USERNAME/Android/Sdk
Replace USERNAME with your user name

Now, Run the react-native run-android in your terminal.