Most difficult procedure to make Query Viewer work is task on Google Developers Console.
Log in Google Developers Console. You must use Google account which you log in Google Search Console.
You will see next dialog if you first log in Google Developers Console with that Google account.
Make sure you agree to terms of service and continue.
After logging in Google Developers Console, create project.
Enter project name (whatever you like) and click "CREATE".
You are welcomed to API Library.
Type in "Search Console". Select "Google Search Console API" from list.
You will see screen shown below.
Click "CREATE CREDENTIALS". This button may be at right side of screen.
Select marked red item exactly same as shown below. And click "What credentials do I need?".
Click "SET UP CONSENT SCREEN".
On next screen, type in application name (can be any but I recommend "Query Viewer") only. Leave other boxes untouched.
Click "Save" at button of screen.
Click "Create credentials" on dialog shown below.
Click "OAuth client ID".
Select "Other" and type in "For Query Viewer" (can be any), then click "Create".
Your client ID and client secret will be show. Copy and paste them to text file. Query Viewer asks you to enter them.
Click "OK" and you finished time taking task.
Note you can view your client ID and client secret anytime from "Credentials" menu item.
How about taking some break.