Double click on the door sprite. Three windows open
1. Sprite editor
2. Animation editor
3. Animation frames editor
In the animation editor you will see an animation called default. You need two animations
1. Default and 2. Open.
To add new animation right click on the animation editor --> add new animation. Name it as open. Select default, leave one frame (door closed image). In open animation import all the sprites where the door opens. So now when the layout is started default is loaded that means the door will be closed. If you want to open the door at any condition then add that event.
On mouse click on object "door".
"door" set animation "open".
Hope it helps