On Safari (iOS), Apple makes it easy to switch. Settings > Safari > Search Engine and select which one you want. I’ve been using DDG not quite a year and at first the change felt a lil jarring, but knowing I’m contributing less to Google’s ad revenue and their long list of privacy violations, I’m comfortable now sticking with DDG. Change isn’t always easy, convenient, or comfortable, but it can be done with just the tiniest bit of effort.