A Handpan Soul account exists only once you sign in with an email code, VK ID, Yandex ID or Google, or pay for access. If you never signed in or paid, there is nothing to delete: everything lives on your device and goes away with the App's data.
Write to support@handpan-soul.ru with the subject "Delete account" from the address that received your receipt or sign-in code. If you signed in with VK ID or Yandex ID, say so. The account is deleted within 7 days and the answer comes to the same address.
Your email, sign-in methods and access rights, including Lifetime, are deleted; installations on all devices are switched off and card auto-renewal stops. If you want a refund for unused time, ask before deleting (offer, section 6).
Purchase records (order number, amount, date, receipt email) are kept for 5 years as tax law requires, unlinked from the account.
A subscription bought in Google Play or RuStore must be cancelled in the store separately: deleting the account does not stop it.