Please specify a platform for this target in your Podfile?

Replace your whole pod file text with below text and then check.

# Uncomment the next line to define a global platform for your project

# platform :ios, '9.0'

target 'testing_gowtham' do

use_frameworks!


pod 'Firebase/Core'
pod 'Firebase/Firestore'
end

(or) solution 2

platform :ios, '9.0' is working...I simply removed # this

# Uncomment the next line to define a global platform for your project
 platform :ios, '9.0'

target 'testing_gowtham' do
  # Comment the next line if you're not using Swift and don't want to use dynamic frameworks
  use_frameworks!

  # Pods for testing_gowtham
 pod 'Firebase/Core'
 pod 'Firebase/Firestore'

end

In your Podfile -> Uncomment platform and set ios : 10.0

    platform :ios, '10.0'

this will work.