https://support.google.com/googleplay/android-developer/contact/key
note that if you are not enrolled in Play App Signing, you will not be able to recover. there are lots of warnings to keep your signing key safe. it is a
signing key - it cannot be recreated without the full private key that was generated before.
also, not kotlin-specific, does not belong in this community slack (see channel description). there are plenty of other fora that better suited for this question.