I was told you can reset dungeons now how do you do it?

Click the button that says "Reset Dungeons".

Gee thanks where’s the button

If you are solo then:

1) Leave the dungeon (by quick key or manually)
2) Exit game (but DO NOT FORCE EXIT GAME, wait for the timer)
3) Start game
4) You are at the entrance and dungeon is ready to go again

Open quest log and you will see the button (square on Playstation)