Steam: Right-click on Kid Hallow in the library list and choose "Properties". Click the "Local Files" tab and then "Verify integrity of game files".
Itch: Open Kid Hallow in the itch.io desktop app's Library. In the bottom-right, click the gear icon. Click "Manage" and then "Check for update".
Steam: Right-click on Kid Hallow in the library and choose "Properties". Click the "Local Files" tab and then "Browse". Levels are in the "local" folder.
Itch: Open Kid Hallow in the itch.io desktop app's Library. In the bottom-right, click the gear icon. Click "Manage" and then "Show in file manager". Levels are in the "local" folder.