View your sequence, and identify the part to which you wish to apply the reverse/adjust speed effect.
Use the two triangular sliders under the preview screen to choose in and out points for your effect (the area where you want to apply the effect becomes marked in yellow).
Click on the Editing button (its in the row on the right, alongside Clips, Themes, Media etc).
Click on the Video FX tab
Click on the item called Fast/Slow/Reverse
Adjust the speed setting as required, and tick the Reverse direction checkbox
Click Apply, (or click on the tick symbol on the preview screen).
The effect will then be rendered in your chosen part of the sequence.