How do I restore the "Quick Start" migration from my iPhone X to a newly bought iPhone 11 Pro Max?

I just bought a new iPhone 11 pro max.

After turning it on and did some very simple settings, it asks me to transfer data from my previous iPhone.

However, I accidentally switched to another app on the previous iPhone. After switching back to the home screen, the popup about transferring data was gone. I could never manage to restart the "Quick Start" feature.

How can I restart the "Quick Start" feature so that I can complete transferring apps from the old phone to my new phone?

You can’t resume an interrupted Quick Start. You can start again by erasing your new phone (Settings → General → Reset → Erase All Content and Settings) which will start the phone back at Setup, where you can begin Quick Start again.

Same thing happened to me. Just restart your old device and the popup should come up again.