You don't need to disconnect your Apple Pencil from your old iPad. The Apple Pencil automatically connects to the iPad it's paired with. When you use your Apple Pencil with a different iPad, it will automatically pair with the new iPad. If you want to use your Apple Pencil with your old iPad again, simply bring it close to the iPad, and it will automatically reconnect.
You can also manually disconnect your Apple Pencil from your old iPad by going to the Settings app on your iPad and tapping on Bluetooth. Then, tap the "i" icon next to your Apple Pencil in the list of Bluetooth devices. Finally, tap "Forget This Device".
This will remove your Apple Pencil from the list of paired devices on your old iPad. Now, you can pair your Apple Pencil with a different iPad.
