Step 1. Add a file
Look for the clip you want to rotate using the "+Video" button or drag-'n-drop option.
Step 2. Rotate the clip
Click the "Edit/Play" button on the right. Press the button "Rotate 90° CCW" or "Rotate 90° CW" to revolve your video left or right respectively. Click "Ok".
Step 3. Convert the rotated file
To save the changes, you have to convert the file. Choose a format (better the same as the original), preset "Same as source", and click "Convert".
Watch our YouTube tutorial "How to rotate a video".