IPhone – Deleting iCloud account with no password entered on the iCloud page

Since you can not bypass the activation lock itself, you need to contact Apple and get control of that account. If you are the original purchaser of that hardware, you might also be able to get them to reset the lock with proof of purchase and identity.

The website https://appleid.apple.com has instructions on resetting your iCloud password if you do not remember it.

You can retrieve the email by erasing the iPhone from iTunes when the device is in normal recovery mode and you will be prompted to enter the password for the email account. Also, if the device is not locked, go to the settings app and look in iCloud for the AppleID that has locked that device for firer activations.

This article looks like it may be your answer. It details how to deactivate your old AppleID in particular. You could also, if I understand your problem, put your AppleID back on the iPhone, turn off Find my phone, then again delete the appleID. Or check this link for ways to do it without having your iPhone set up again.

https://www.macrumors.com/how-to/how-to-delete-or-deactivate-your-apple-id-account/