Table collection with Google sheet extension: Add default columns and pull from sheet via script

Add default columns and pull from sheet via script is possible?
I want to do these things below.

Code (CSharp):

1. public void PullFromSheet()
2.     {
3.         foreach (StringTableCollection collection in LocalizationEditorSettings.GetStringTableCollections())
4.         {
5.             // 1. Get google sheet extension from extensions
6.             // 2. Add default columns to mapped columns
7.             // 3. pull from sheet
8.         }
9.     }