You can rotate any images in Dash that are JPEG, PNG or WEBP format by doing the following:
Open an asset by clicking on it in the "All assets" page
Click the three-dot menu in the menu bar
Click rotate
Use the rotate buttons that appear over the image to rotate the image either clockwise or counter-clockwise
Click Done when happy!
Each time you save a rotation will save the asset as a new version, which you can find and manage in the versions panel.
Why am I not seeing an option to rotate my image?
Dash is only able to rotate the file types listed above - JPG, PNG or WEBP. Any other file types, such as HEIC, are not currently supported.