Diabox will keep on reading your old sensor for 12 more hours after the libre app says your sensor has ended.
So while you wait for the 60 minutes warm up after you've started your new sensor with either Librelink or the reader, you can still read the values on DiaBox.
After the warm up hour you can scan the new sensor and DiaBox will ask you if you want to start a new sensor. Select yes and it's running again!
Sometimes it takes a couple of hours for DiaBox to pick up the new sensor but you can still scan with the Libre app.