Earlier quoted context omitted.
I don't use an iPhone so have to ask, can users not select the search engine they want to use? Oneplus tried to change the default search on their phones to Bing and the first thing I did was switch back to Google.
On iOS — in contrast to Android — you can actually change the default search provider, yes. (On Android you can't change it at all. And so I'm either stuck with a Google search on the Recents menu, or the "this widget could not be found" message)
If you're talking about at the Google Now or Siri then as far as I know that's not possible on either OS.