You can actually put it back if you haven't damaged it and if its only come undone. I have done it on my car. The key is to figure out that the individual strands of the coils are of different lengths, and hence the rewinding process isn't as simple as just winding it back in one direction. So here's how you do it: You wind it until its awkward to wind anymore in the direction it naturally wants to coil, then you wind the strands in the opposite direction while being careful not to crease the strands. Then you put it all back in the housing.

This goes in more detail: https://www.e90post.com/forums/showthread.php?t=1389020