As mentioned, there is nothing we can do while working in Build mode, but don't panic because it is possible to control or at least use an imported animation.
Tip
A word of caution: the process, although not complex, involves good planning and use of layers to hide and show animations.
In order to work with imported animations, there is one essential question you need to answer: how long is the animation?
This is information you really need. Why? Let's say the imported animation is in total 8 seconds or 200 frames. It is imperative that the clip you create is only 8 seconds long. Why? Because if the clip isn't 8 seconds long and the object is still on frame, you will see the 3D model going back to the original position and repeating the same animation.