Hi fang16,
Longedge is right but I find it easiest to use 'Edit Using Content Aware Editing...'
because here you can 'Select' and 'Deselest' any part of your video clip.
You can choose 'Edit Using Content Aware Editing...' either in the media room or at the timeline by Right-Clicking on the video clip.
PDR 14.0.4207.0 / Windows 10 64-bit / Asus / Intel i7-4790 3.60 GHz / 16GB RAM / NVIDIA GeForce GTX 970 / DirectX 12