If your Google Merchant account only has a 'promotions' tab under your Marketing tab, you will have to submit a 'Product Ratings Interest Form'.
If you haven't completed this form, you will not have the 'product review' tab.
⚠️When filling out the form, please follow this step⚠️
Under 'Do you work with an approved third-party reviews aggregator?'
Select 'No'
Google will approve or deny your application to have a reviews feed.