Use this if you don't have yet categories set for your products, or to improve your existing product categories.
Step 1: click on "+Product Categories" button:
Step 2: choose between Default Settings and Advanced Settings:
Default Settings: Categorize based on the title (+description columns).
Data Columns: Which columns to use for the data to predict categories
Top Category: Select if the entire feed has just one base category, e.g. Health & Beauty.
Category level: How many category levels will be included. e.g. if 2 is selected: Apparel & Accessories > Jewelry
Step 3: click "Apply".
"Clear" will remove the action.
Now a new column named "Google Product Category" is added to your feed view.
Don't forget to save!