Master of Potions

Hello all, im trying to get the Botanist's Field Guide for the quest "Master of Potions" and i need to get into Botanica to obtain the item. When i try to enter to the instance it doesnt allow me cuz i need a key to enter the heroic mode.. How can i enter the normal mode??

Right click your portrait and hover over instance difficulty. Change it to normal, when you want to enter a normal dungeon, heroic for heroics ofc.