Hey kiraiaoshikage3!
There's 2 locations for saves/progress on PC for AHITR.
Where your game folder is located, you'll have a "game" folder where the .exe is. Inside the "game" folder you'll have "saves".
Example: C:\AHouseInTheRift-GameVersionHere\game\saves
There's a backup folder in your "appdata" folder that your saves get synced to. You can find it in the example below:
C:\Users\Name\AppData\Roaming\RenPy\AHouseintheRift
Alternatively you can hit Win + R and type "appdata" from there open "Roaming", then "Renpy" and then "AHouseintheRift"
Make sure to delete both of these locations (including any "sync" folder or "persistent" file).
Deleting these will completely delete all your saved data. (I'd make a backup of your saves just in case).
On Android your saves will be in "ahitr_storage" and the "sync" folder.