I restarted my iPhone 11, can’t remember the 6 digit code to unlock device. Now says I cannot try for 8 hours. My other iPhone 11 Pro Max on cellular network has that iPhone under same Apple ID. How can I unlock my iPhone (only used on Wi-Fi)?

can’t I use my iPhone to unlock red iPhone?

Sorry, but no.

You will have to wait until an Unavailable or Security Lockout screen appears on the phone, then use the instructions in the Apple Support document below to erase and reset the phone. Use your current backup to restore the phone again.

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

Might be a good idea to write down the new passcode and keep it in a safe place, even though you might be sure that you will never forget it.