How do I go about reimagining a sound?

There are many approaches you can take, the most basic being simply to edit, filter and add effects to the existing sound, then save it! You can be as simple or as complex as you like – you could even take the original sound and add some of your own music to it, without editing the sound at all. There’s a list of simple and free tools for editing sounds over here. Even if you felt inspired, for instance, to record yourself reading a poem over the original, that would be equally valid. The most important thing is to reflect your own personal interpretation of that sound. There’s a good summary of some of the many creative approaches other artists have taken to reimagining sounds here.