In AirBox:

Make sure the Clip Trimmer is enabled in Settings menu > General > þUse Clip Trimmer.
Double-click in a clip to open the Clip Trimmer;

Select the In and Out points using the position marker or in the relevant time code box and click OK/Apply to enter the changes in the playlist.

Right-click in a clip and select Edit… from the drop-down menu or press <Alt> + <Enter> on your keyboard.

Select the In and Out points using the position marker or in the relevant time code box.
Click Apply to enter the changes in the playlist.