Deleting inactive Apple ID on iPhone

You are encountering Activation Lock, a mechanism intended to deter theft. It uses intentionally difficult to bypass. We can’t help, and — absent evidence of ownership sufficient— Apple won’t.

You’ll need to regain access to that Apple Account and release the lock, or provide evidence of ownership sufficient to convince Apple. That’s usually an original purchase receipt from Apple or an authorized reseller.

Without either of those, this iPhone is indistinguishable from a lost or stolen device.

• How to use account recovery when you can’t reset your Apple Account password - Apple Support
• How to remove Activation Lock - Apple Support

iCloud uses Apple ID credentials.

If you do not remember the Apple ID Password then follow the steps given in this Apple Article -> If you forgot your Apple ID password - Apple Support

If you do not remember the Apple ID then follow the steps given in this Apple Article -> If you forgot your Apple ID - Apple Support

If you are the owner or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their Apple ID.