Capture One reads the image file's metadata to automatically orient the image to that set in the camera. If that data is not available or readable, Capture One provides several options to orient your images quickly.
Shortcuts to the Rotate All Selected Variants Left or Rotate All Selected Variants Right are available in the main toolbar. If there are no such icons present, right-click on the toolbar, select Customize Toolbar, and drag those icons.
The Rotate Left or Rotate Right cursors are available via the Rotate cursor group in the cursor toolbar.
You can also find those in the Rotation & Flip tool.
The shortcuts and cursors rotate images through 90-degree steps, so if the wrong one is selected inadvertently you can apply it several times to orient the image correctly. The cursors can also be used on thumbnails in the Browser, bypassing the Viewer and making it easier and quicker to orient occasional non-contiguous images without selecting them first.