Disconnect Apple Pencil
Press the pen icon while the pen is activated and open the pen options. (You can do the same thing with the lasso tool)
Press the Disconnect Apple Pencil button at the bottom and then the Apple Pencil will be disconnected.
Re-connect Apple Pencil
To re-connect Apple Pencil, open the app and touch anywhere on the screen with Apple Pencil.
※ To re-connect Apple Pencil, you should pair your device with Apple Pencil.