Open Project in Xcode
If Xcode > 9
run command react-native upgrade
(this overwrites all your iOS configurations, use with caution!)
then
1.Go to File -> Project settings
2.Click the Advanced button
3.Select “Custom” and select “Relative to Workspace” in the pull down
4.Change “Build/Products” to “build/Build/Products” and “Build/Intermediates” to “build/Build/Intermediates”
5.click done, done