DNS/Androidについて、ここに記述してください。
Android Configuration instructions for OpenDNS
These instructions only work for Wi-Fi connections because Android does not allow you to change the DNS servers when connected to cellular networks.
Wi-Fiごとに決められるらしい。
How to make Android use the DNS server of your choice Stephen Schenck
https://www.androidpolice.com/2018/04/20/make-android-use-dns-server-choice/