There are three ways of managing bids for product groups in shopping campaigns. Based on your requirement you can choose one or a combination of the options mentioned below.
Shopping Bidder - Manage Bids
This is the most basic way of managing bids for product groups. You can change bids in bulk based on performance. For example, you can choose to bid higher on product groups that have high ROAS but are losing impression share. Bids can be increased or decreased by a number or percentage. Or, you can set them to a specific number. Use case: This comes in handy when you want to make standard bid changes across shopping campaigns. For example, if you created a new shopping campaign with 10,000 product groups and you want to start all product groups off with a bid of $1.00, you can use this. Or, if you want to reduce the bids for all non-converting product groups by 10%. Read more about this tool here.
This is perhaps the most versatile tool we have to manage bids. It lets you change bids for product groups, keywords and ad groups based on performance. It gives you a lot more flexibility in terms of comparing performance and also when setting bids. For example, you can change bids for product groups that have a lower ROAS than the ad group average and then choose to set the bid using your target ROAS and conversion rate. To get started you can use one of the instant strategies (templates) to bid by target ROAS. It also offers advanced options that let you use external data like sales or profit margin date to make bid changes in Google Ads. Read more about this tool here.
Product Attribute Bidder
This is a more advanced way of analyzing product group performance and changing bids. This tool lets you combine performance data from Google Ads with attributes from your feed. It aggregates performance of product groups across the campaign based on attributes from the feed. For example, you can combine data by Brand ->Product Type 0 ->Price. This enables you to set bids for product groups based on price. The only requirement to use this tool is to have one item id per product group as that lets the tool group data any way that you want. If you don't have this structure, you can use the Create GRIP structure tool. Read more about the Product Attribute Bidder here.