If you want to rotate a file from the file display (e.g. via the right-click menu, or a lister toolbar or lister hotkey), use this as the command:
Image ROTATE=90 HERE REPLACE QUALITY=75
If you want to rotate the file in the image viewer (i.e. rotate the actual file on disk, and also update the orientation in the image viewer), put this on the viewer toolbar, or viewer context menu, or a viewer hotkey:
Image ROTATE=90 HERE REPLACE QUALITY=75
Show VIEWERCMD=refresh
(The first line is the same in both commands. You can change the QUALITY value if you want; it's only used when rotating JPEGs, although they will usually be rotated losslessly anyway, unless they have unusual dimensions etc.)
Commands are from this post, which is from 2017 but still correct: