How can I edit data for sleep analysis in the health app?

I added sleep data in the Health app after clicking Sleep, then Add Data (the "Starts" switched to AM, so the interval added turned out to amount to almost the full day). The statistics got all wrong, so I repeated the step using "Awake" - however, this still makes the app think my sleep schedule was about all day, and all the graphs now are scaled down because this single entry (graphs now show the full day, instead of say 9-10 hours).

Please, dont tell me to click Edit, or Show more data and then click Edit because there is no Edit option, only Add. Any help is appreaciated, thank you.