The savefile is stored locally as a cookie for the domain graphomata.com, so deleting it will reset all progress.
Alternatively, you can start from this empty savefile (equivalent to deleting the cookie and reloading the page).
Instructions for the former (for desktop browsers):
- Chrome: Settings -> Privacy and security -> Site Settings -> graphomata.com -> Clear data
- FireFox: Options -> Privacy & Security -> Manage Data -> Cookies and Site Data -> Manage Data -> graphomata.com -> Remove Selected
- Edge (newer versions): Settings -> Cookies and site permissions -> Manage and delete cookies and site data -> See all cookies and site data -> graphomata.com -> expand icon -> trash icon
- Edge (older versions): More tools -> Developer Tools -> expand icon -> either Debugger or Storage -> Indexed DB -> graphomata.com -> context menu -> Delete cookie
- Safari (not tested): Safari -> Preferences -> Privacy -> Manage Website Data -> graphomata.com -> Remove
- IE 11: Tools -> Internet options -> General -> Settings -> Caches and databases -> graphomata.com -> Delete