Hello there, maysamsh.
It seems you're having an issue where you need to receive an activation code for iCloud Keychain and no longer have access to another registered device. The following Knowledge Base article offers up some great recommendations:
Frequently asked questions about iCloud Keychain
Set up iCloud Keychain for each device that you want to add. When you turn on iCloud Keychain on an additional device, your other devices that use iCloud Keychain receive a notification requesting approval for the additional device. After you approve the additional device, your iCloud Keychain automatically begins updating on that device.
If you can't access any of your other devices that are using iCloud Keychain, you can still set up iCloud Keychain on another device if you have these items:
- Your iCloud Security Code
- The device that is using the SMS-capable phone number you provided when you first set up iCloud Keychain. A verification code is sent via SMS to this phone number. If you can't access this number, contact Apple Support, who can verify your identity, so that you can complete setup on your new device.
After you complete the setup, your iCloud Keychain will be pushed from the cloud to the new device.
Thanks for being a part of Apple Support Communities.
Cheers.