There are four different difficulties for all story missions.Originally Posted by Cutaway2019 Go to original post
You can not change tiers but you can set global difficulty to four different difficulties. Basically the same thing.
Is this a L30 character? There is a bug where L30 characters can only change mission difficulty from the world map.Originally Posted by Cutaway2019 Go to original post
You cannot change world tier.
Continue doing Campaign ( World Tiers ) and they will unlock more as you progress.Originally Posted by Cutaway2019 Go to original post