Updating products in bulk with a data ingestion contrasts to updating products on a record-by-record basis using the "edit" forms.
Create a new Google Doc using the products-default-template file (See menu item: File > Make a Copy…). Name the new file as you deem necessary, but omit spaces (e.g., products-default-YYYYMMDD where YYYYMMDD is today's date).
When the new file is complete, download the data as a CSV file to your local machine. Follow the same naming convention as in step 1, but add a ".csv" extension (e.g., products-YYYYMMDD.csv).
Navigate to the new ingestion form.
Select the appropriate ingestion type.
Choose the local CSV file to ingest.