Withered Army Training question

[Harry Botter]

I was making decent progress on keeping my dudes alive but now when I get into the first room down and to the left with the boss in it there is long longer a chest in there and I have no idea how to get more berserkers to open to big door on the right. Can anyone please provide me with help or what I am doing wrong?


Edit....im an idiot as soon as i posted this I saw what I wasnt seeing before.....