In Step 2 - Edit, you have the option to adjust many characteristics of a selected video clip. You can reset all of those back to the default at any time by clicking the "Reset All" button at the bottom of the Settings panel.

If you want to reset only a specific setting back to default, you can click the title of the setting and it will reset that setting to its default. For example, if you make a change to Exposure and you want to reset it, just click on the word "Exposure."