How to rotate a video on Google Photos

How to rotate a video on Google Photos?

Facts:

• There is no option for this at photos.google.com
• Sometimes it's also not working on the cellphone - why?

Solution

• Select the video on your cellphone with the Google Photos App
• open the menu (top / right) and select 'download' (or sometimes 'restore')

• Wait till it has been downloaded, then push the 'pencil' button:

• Now you have the 'rotate' option available, but before you start, please press the (i) button and write down the date / time of your recording - you will later need it to correct it. 

• Don't forget to save this 'action':

• And at the end goto photos.google.com, select your video, click on the info-button (i) and restore the original date / time (enter it manually).