Mine was also loose, and I figured out how to get it back in.
First, you have to imagine how it was pulled out in the first place.
When the spring was pulled under excessive tension, the diameter of each coil was decreased.
You can imagine a spring being pulled with maximal tension, it is essentially a single strand of wire.
So, to get the spring back in, first take your fingernail and pull down the last rung of the spring, while pulling the rest of the spring away from the hole. This first step is to separate the last coil enough to get it caught underneath the lip of the hole.
Then, while keeping your fingernail there as a guide and to provide resistance, pull the spring away from the hole while rotating the spring in the direction of the coil, to "screw in" the rest of the large coils. Make sure to pull on the spring enough so that the diameter of each coil is small enough to be easily screwed into the hole. When you have finished doing this for all the large coils, you will feel the spring slip and it's in place.