To reverse a single clip, right-click on it and choose REVERSE CLIP.
To reverse an entire project...
1. Click the + to the right of the SEQUENCE 1 x tab above the timeline. This will create a new, blank sequence.
2. In the bin (top-left) click the SEQUENCES tab.
3. Drop sequence 1 from the bin onto the timeline. It's now a single clip.
4. Right-click and REVERSE CLIP.