if you mean when searching in the address bar or "omnibox" as they seem to call it:
click the three lines at the top right corner, settings, (a new tab will open), the 4th group down is Search, you're set to Ask, just change it to Google. Just close the tab, it saves the change instantly.
If you mean the home page, also go to 3 lines, settings, and the second group "on startup" select "open a specific page or set of pages" and then click Set Pages. hover over any pages you don't want to open at startup and click the X to remove, and in the box for Add New Page, enter
http://www.google.com/ then click ok, and close the tab.
If you mean something else, let me know exactly what you want and I'l try to help.
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