In Google Ads, click Edit on the campaign or ad group and open Audiences. When the strategy supports it, each connected audience displays a percentage adjustment field. After saving, Ads Editor shows the previous and new values. You can also reach it from the Segments tab under Audiences for this campaign.

With automated strategies and Performance Max campaigns, Google normally uses the audience as a signal and may not accept an adjustment. In that case, use Targeting to deliver only to that audience or exclude an audience you do not want to reach. The screen shows the actions supported by the current strategy.