DuckDuckGo users in India are currently facing problems in connecting to the site, and it looks like that the site has been blocked by ISPs.
How to change the default search engine in Microsoft Edge browser? Add and use Google Search, DuckDuckGo, Yandex and others.
Learn how to change your default search engine on Firefox browser for Android. You can easily set DuckDuckGo as your default search engine, which is considered to be most privacy-friendly.