Open Title Buddy with /tbconfig.
Select the zone for which you’d like to save a title: open world, dungeon, or battleground. Whenever you enter this zone, a button will appear, allowing you to instantly activate your saved title without needing to search through the character window.
Repeat the step with /tbconfig for each zone where you'd like to add or change a title.
If you choose the same title for two zones, the button will not appear if the selected and saved titles already match. You can also set the same ID for all three zones to avoid Blizzard's occasional bugs, which sometimes cause titles to disappear.