How to re-enter the lock code through NULL ?

Hi there AliAmerah,

If you are seeing a message that your iPhone is unavailable, these steps from If you see an iPhone or iPad unavailable message or Security Lockout screen walk you through what to do:

How to reset your device

If you're using an eSIM, contact your carrier before trying these steps and ask for a QR code to set up your eSIM again.

1. From your device's Lock Screen, try to enter your passcode five times until the "[Device] Unavailable" screen appears and your device asks you to try again later.

2. When you're able to, continue to enter your passcode until the "Security Lockout" screen appears and you get the Erase [Device] option in the bottom corner of the screen.

3. Tap Erase [Device], then tap Erase [Device] again to confirm.

4. Enter your Apple ID password to sign out of your Apple ID on your device.

5. Tap Erase [Device] to permanently delete all of your data and settings.

6. When your device restarts, follow the onscreen instructions to set up your device again, restore your data and settings from a backup, and set a new passcode.

If you can't follow these steps, you can use a computer to reset your device.

You can only reach the "Security Lockout" screen if you have an active cellular or Wi-Fi connection and previously enabled Find My on your device. After you try to enter your password ten times, your device will either erase itself or show Security Lockout and the option to Erase [Device] without a timer, depending on how you previously set up your device. 

Once the iPhone has been fully restored, you can recover your data from an iCloud or computer backup using this article: Restore your iPhone, iPad, or iPod touch from a backup

We hope that helps!