Follow below mentioned steps to get your Google Client ID and Secret Key:
Step 1 : Go to Google Developer portal
Step 6 : Click on Enable APIs and Services
Step 7 : Search for Google Play Android Developer API here. You can even scroll down to Mobile section.
Step 8 :Click on Google Play Android Developer API
Step 9 : Click on Enable to activate the key
Step 10: Click on Credentials
Step 11: Go to OAuth Consent Screen
Step 12: Enter Application Name, Authorized Domains .Once you are finished, click on Save to continue
Step 13: Open Create Credentials dropdown menu
Step 14: Click on OAuth Client ID
Step 15: Select Web Application here
Step 17: Here is your Client ID and Secret Key.Copy them
Step 18: Paste the copied keys in the respective fields on the creator software and click on connect.
Step 19 :Go to Google Play Console
Step 20:If you have a Google Developer account, login, else Signup
Step 21: Go to Settings
Step 22: Click on API Access under Developer Account
Step 23: Here you will see all your projects. To access the API, you need to link your account to one of your Google Developer project. Select your desired project and click on Link. You can even create a new project by clicking on Create New Project
Step 24: Here you will see the project linked.