You should see a section labeled Search engine used in the address bar with a dropdown menu. You can pick from Bing, Yahoo, Google, DuckDuckGo, and YouTube by default. You can also click Manage search engines, then click the three dots next to the search engine you want to use and click Make default.

Perform a search in the address bar using the search engine you want to set as your default. Select Settings and more > Settings. Select Privacy, search, and services. Scroll all the way down to the Services section and select Address bar and search. Choose your preferred search engine from the Search engine used in the address bar menu.