The Monster-Handlers can certainly reset your account's progress for you; however, there is no way to recover it later. It is strongly recommend to create a new account instead:

iOS

1. Uninstall My Singing Monsters
2. Disable your iCloud backup and restoration
3. Restart your device
4. Reinstall My Singing Monsters
5. Select the Guest login method to create a new account

Android

1. Open your Device Settings
   
2. Select or search for "Accounts" (may be located in "About Phone")
   
3. Select Google
   
4. Select "Remove Account"
   
5. Uninstall My Singing Monsters
   
6. Open the Play Store
   
7. Sign into your Google Account
   
8. Reinstall My Singing Monsters
   
9. Launch My Singing Monsters
   
10. When prompted to sign in with your Google Play Account, tap "Cancel"
    
11. Select the Guest login method to create a new account

Amazon

1. Uninstall My Singing Monsters
2. Clear app cache & data
3. Restart your device
4. Reinstall My Singing Monsters
5. Select the Guest login method to create a new account

Steam

1. Create a new Steam account
2. Launch My Singing Monsters to create a new account