Hi RoGirl
This message is nothing to worry about.
Windows "manages" your default printer by changing the default printer to the one you use most often.
When you set the default printer manually, windows is simply telling that it will not change it automatically.
you can set it back to managed by Windows at anytime if you wish.
settings -> Bluetooth & Devices -> Printers and Scanners
turn on "allow Windows to manage my default printer"