Photo manager has some very basic image editting functions - the image rotate buttons at the bottom of the window only rotate the display of the image if you just click an image and then the rotate buttons.
However there is a way of doing rotation as follows:
Select the image to be rotated
Click the green Optimise button or press Shift + v to activate the Optimisation window
Rotate the image using the buttons at the bottom of the screen.
Leave the Optimisation screen by clicking on another image, you will be asked what you want to do with the altered image.
It is not rotation I was after but a way to flip images. Rotation spins an image around a central point. Flipping an image turns it over a centreline, ie as if the image were to be turned edge over edge.