How to retrieve data from old iPhone 12 to new iPhone?

Without your old phone being able to turn on, you will not be able to use the Quick Start option to transfer data directly from the phone, but you will be able to restore it from an iCloud backup as long as your old device was being backed up before it broke.

Set up your iPhone or iPad - Apple Support

You can set up your new phone using your iCloud backup of your old device

Jewels6989 Said:

"My old iPhone 12 won’t turn back on had to get a factory new one how do I get my old data on my new phone"

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Troubleshooting an iPhone not Turning On:

"won't turn back on". How So?

Is it not powering on, or are you unable to get back in? If you cannot get back in, then it may be stuck in a Boot Loop. See Here If your iPhone is Stuck on the Apple Logo - Apple Support

Fixing a Boot Loop:

Your iPhone can at time be stuck in a Boot Loop. This typically occurs when you go abuut installing an update, and it stalled while in the process. Go here to fix that: How to Fix an iPhone in a Boot Loop - User Tip

I. Perform a Restart:

A. Try Force Restarting your iPhone:

Save any information that need be. Then perform the restart.

Go Here: Force Restart iPhone - Apple Support

B. Try Manually Restarting your iPhone:

1. Go To: Settings
2. Select: General
3. Scroll to: the Very Bottom
4. Select: Shut Down
5. Slide Finger: to the Right
6. Wait: 30 Seconds
7. Power One: the iPhone
8. Try this Once More

II. A Few Apple Support Sites that May Help:

• iPhone Battery and Performance Apple Support

• Charge and Monitor the iPhone Battery Apple Support

• About the Battery Usage on your iPhone - Apple Support

• About Optimized Battery Charging on your iPhone - Apple Support

• If you see "Your iPhone Battery May Need to be Serviced" - Apple Support

• Use Low Power Mode to Save Battery Life on your iPhone - Apple Support