It's not currently possible to 'reset' an account once data has been added. It would be necessary to go through and manually delete each entry. Because this can be a slightly tedious process depending on the amount of test data, we generally suggest deleting the test account and creating a fresh, new account.
You can delete your account at any time under 'Settings > Account > Delete account'.
Unfortunately we cannot do this on your behalf.
For a step-by-step guide to deleting an account, please follow the steps in our short guide here: https://debitoor.com/tutorial/settings/delete-your-account