First, you'll need to upload your clip. You can drag and drop clips directly from your computer into Runway, or sort through the Assets section on the left side of the editor if you've already uploaded them. For more information on what kinds of video formats we accept, see here.
After your video is uploaded and placed in the editor timeline, click on it once to ensure it is selected, and then use the Speed adjustment slider in the right-hand panel to decrease the speed to your liking. Then, simply click the checkbox beside Smooth Slo-Mo. It may take some time to process. Enjoy your smooth slow motion results!