I am using DaVinci Resolve 15 Free version. How do I rotate video in it? I tried Clip Attributes, and I see an Image Flip feature, but not rotation.
You need to place the media in the timeline, select the clip and pick the Inspector. There is a rotate feature in the Transform tab.
In detail (assuming you are in a project and the media has been imported):
After the rotation, the video might not fit the entire screen. You will have to zoom based on the ratio of project_width_resolution/clip_orig_width_resolution.
For example, I have an ipad video at 1440x1920. The project resolution is 1920x1080. I will have to zoom at 1920/1440 = 1.33333