Information applies to Safari on iOS devices with iOS 14 through iOS 10.
Scroll down and tapSafari.
The current default search engine is listed next to theSearch Engineentry.TapSearch Engineto make a change.

Choose a different search engine from four options: Google,Yahoo,Bing,andDuckDuckGo.
TapSafariin the top left corner of the Search Engine screen to return to Safari’s options.
The name of the search engine you chose appears next to the Search Engineentry.