Double-click on the clip in your timeline (bottom middle of your screen should have thumbnail icons of the clips in your project). This will open up a new page - clip editor mode!
Above the clip timeline, click on the ‘Crop’ button.
This opens up a menu where you can:
Make your clip fit or fill the canvas: a fast way to adjust the clip position and scale
Fit = clip will appear in full within the frame and will not crop the footage
Fill = clip size will cover the entire frame and may crop the footage
Adjust the clip position: type in a number to move the clip in the canvas
X = negative # (left) or positive # (right)
Y = negative # (up) or positive # (down)
Ex: X = -10 and Y = 10 would move your video 10 spaces to the left and 10 spaces down, closer to the bottom left corner of your canvas.
Scale your clip size: zoom in or out
Higher than 100% = cropped
Less than 100% = not cropped, background will be visible
Click on the checkmark to save your changes! Clicking on the X will discard your changes.