To edit a Multicam Clip in ScreenFlow, you first need to create a Multicam Clip. You can do this by selecting all the clips you want to include in the timeline, then right-click and choose "New Multicam Clip". This will create a new clip that combines all the selected clips into one.

Once you have your Multicam Clip, you can edit it by double-clicking on it in the timeline. This will open the Multicam Clip in a new tab, where you can see all the individual clips that make up the Multicam Clip. You can then select the clip you want to edit and make your changes. You can cut, trim, add effects, and adjust the audio and video settings as needed. When you're done editing, you can close the tab to return to the main timeline, and your changes will be reflected in the Multicam Clip.

Remember to save your project regularly to avoid losing any changes. ScreenFlow also has an auto-save feature that you can enable in the preferences to automatically save your project at regular intervals.