You want to add pod 'gRPC-C++', '~> 1.58' similar to the following to your Podfile:

target 'MyApp' do
  pod 'gRPC-C++', '~> 1.58'
end

Then run a pod install inside your terminal, or from CocoaPods.app.

Alternatively to give it a test run, run the command:

pod try gRPC-C++