Whenever you have duplicate ads in the same ad group, you will see a corresponding alert under the Audit Alerts / Ads tab on your Dashboard.
You can either pause duplicate ads which have received fewer impressions in the last 30 days right from the Dashboard by hitting the button Pause lower volume ads or click on the button View duplicate ads to conduct the analysis and decide how to best solve the issue. In the list of adgroups with duplicate ads, click on each group to see its ads.
Inside each ad group, you will see a warning sign next to the duplicate ads (1). You can either pause the unwanted ad (2) or go back to the list of adgroups (3) to use the bulk pause tool.
You can bulk pause the duplicate ads by selecting the adgroups where the duplicates are and then using the bulk pause tool as shown below.