Welcome to Android Central! I moved this from the OnePlus 5 forum to the General Help forum, since we don't have a specific forum for the Nord line.
What settings have changed? Which OnePlus Nord model do you have? You should be able to access the Power menu by pressing and holding Power and Vol Up together for about a second. But rebooting usually won't change settings back. Again, it depends on what you mean by your settings having changed.