There is no official "New Save" button in-game. Manual file manipulation or reinstallation is required. Always back up your existing save before attempting a reset if you wish to return to it later.
Darkrise often allows multiple character slots. Instead of resetting your main hero: darkrise save file new
Darkrise typically stores save data locally on your device, meaning it is not always automatically synced to the cloud unless you use a specific login method provided by the devs (like Google Play Games). There is no official "New Save" button in-game