When there is no visual reference or you simply prefer to adjust by eye, manual rotation of images is possible using either the Rotation & Flip tool's Angle slider or by clicking and dragging the image with the Rotate Freehand cursor.
Use Shift-R to switch between the cursors in the group. The Grid Overlay opens as well.
- Go to the Lens tool tab.
- In the Rotation & Flip tool, alter the rotation by adjusting the Angle slider.
- Alternatively, long-press the Straighten (R) icon in the tool or cursor tool-bar and select the Rotate Freehand option.
- Once Rotate Freehand is selected, go to the Viewer and click and drag the image to the desired angle.