Click the Post Options Ellipsis.
Select Edit Thumbnail.
Click the Edit Thumbnail icon.
Select Edit Crop + Zoom.
Edit Crop + Zoom as desired and click Save.
Click Update.
Click the Post Options Ellipsis.
Select Edit Thumbnail.
Click the Edit Thumbnail icon.
Select Edit Crop + Zoom.
Edit Crop + Zoom as desired and click Save.
Click Update.