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As automated bidding doesn't allow any external modification, the way to optimize the campaign's performance is by modifying the target Cost-per-Acquisition (CPA) or Return on Ad Spend (ROAS) values at the ad group level. 

Optimizing converting ad groups that are losing impression share due to low ad rank, allows Google Ads to set a better bid at the time of auction.

The Optimize Target CPA & Optimize Target ROAS tools were created using the Rule Engine. 

Google Ads automated bidding doesn't allow manual bid changes and therefore limits the control you can have on your keywords, product groups, etc. Through the use of the Optimize Target CPA & Optimize Target ROAS tools, you can increase conversions by boosting the Target CPA or lowering the Target ROAS when ad groups with conversions are losing Impression Share or with a ROAS above the target/CPA below the target.

You can access the Optimize Target CPA tool here and the Optimize Target ROAS tool here. The following instructions work the same on both tools.

On the left side, choose the campaign and strategy you want to optimize, and press update. You'll see data displayed for Target CPA (current), Target CPA (suggested new), Bid Strategy Type, Conversions, and Search Lost IS. Once you've reviewed this, head over to the Apply button to make the changes.

You can download the suggestion results as a .CSV file as well, even if you don't apply the changes. Inside the file, you'll see two extra columns: Min. Target CPA and Max. Target CPA.

The Optimize Target CPA & Optimize Target ROAS optimizations are built using the Rule Engine, and in order to return a suggested Target CPA that preserves certain boundary values, it creates two metrics: Min. Target CPA, and Max. Target CPA.

These two extra columns are, therefore, not benchmark metrics but rather set boundary values.