Hi! Thank you!
Do you mean that you'd like to remove the ability to skip scenes already played? If so, Ren'py hard-saves your save files to your C: drive. To fully wipe your saves from your system you need to navigate to: C:\Users\*YOURNAME*\AppData\Roaming\RenPy and delete the When The Night Comes folder. This should give you a totally clean, new game with no saves, no CGs etc.