I suggested taking it to the shop to have the bike completely looked over. The spring itself can easily be popped into place in under a second.

**Update**
Look at this video... I modified the URL to start at 159 seconds into the video where the 'instructor' shows how the spring can be popped out of place... do the same in reverse to pop it back in. When you have spare time I suggest watching instructional videos and learn how to perform even the most basic maintenance procedures.

http://www.youtube.com/watch?v=Q8dkU5NhCVY&t=159