To get Google back as your search engine, you need to remove that extension. Go to Extension Manager on Chrome Here you will see the list of all your extensions In order to check the extension which is causing this, simply turn off the toggle Once you find out the extension, click on remove to delete the extension from your Chrome Browser.

Launch Chrome, select the three dots in the top-right corner, and choose "Settings." In "Settings," on the left sidebar, click "Search Engine." Then, on the right pane, choose "Manage Search Engines and Site Search." Scroll down to the "Search Engines" section. Here, next to a non-Bing search engine, click the three dots and choose "Make Default."