how to reset old passcode for old iphone 11 from new phone

You cannot reset the passcode of the old phone from the new phone.

Set the new phone aside and follow these instructions to reset / erase the old phone and then set it up again with a new passcode.

If you forgot your iPhone passcode - Apple Support

To unlock your iPhone, follow the steps described in the Apple article:

(< iOS 15.2) -> If you forgot your iPhone passcode

If you forgot your iPhone passcode - Apple Support

• If you don't have a computer and you can't borrow one, you need to go to an Apple Retail Store or Apple Authorized Service Provider for help.

(iOS 15.2 and newer) you don’t need to have a computer -> If you see an iPhone or iPad unavailable message or Security Lockout screen

If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

Temporarily use your old passcode when you forget your new passcode on iPhone or iPad

Temporarily use your old passcode when you forget your new passcode on iPhone or iPad - Apple Support

• In iOS 17, iPadOS 17, and later, Passcode Reset helps you maintain access to your phone if you forget your new passcode.

Or see: