What should I do when the phone shows “Unlock after Factory reset” after factory reset the phone?

The reason that the phone shows “Unlock after Factory reset” is that the phone is locked by Google. You may need to insert the previous screen lock password that you have set or sign in to the Google account that you have signed in to unlock it.

1. If you remember your Google email address but can't remember the password, you can reset your Google password at www.google.com. It can take up to 24 hours for a new password to sync with all registered devices. After 24 hours, you can try logging in to your phone with the new password.

2. If you have multiple Google Accounts, and you can't remember which Google Account you set up on the device, please visit www.google.com/android/devicemanager to check the list of devices registered to the account.
Log in with your Google email address and password and check the list of devices registered to the account. If you don't see the device listed on the account, it means the device is registered to a different account. Use the same process to check for devices linked to your other Google Accounts. When you find the registered account, use it to log in to your device. 

3. If you can't remember any of your Google Account information, you may provide proof of purchase of the device, and contact the after-sales service team for further assistance.