If the update process has stalled - and the iPad is unresponsive - you will need to restart the iPad:
Force restart iPad (models with Face ID or with Touch ID in the top button)
If your iPad doesn’t have the Home button, do the following:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button.
- When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)
Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

While performing the transfer/update process, keep both iPads connected to their respective Power Adapters throughout the process. Doing so will keep their WiFi connections active.