Freestyle Libre 2 and 3 come with alarms configured by default. You can turn most of the alarms off by doing the following:
Open up the Freestyle Libre App
Click on the 3 lines on the top left and then Alarms
Then you can click on the specific alarm and toggle it off. NOTE in the US can not toggle off the low glucose alarm but can set the threshold to the minimum allowed.
Workarounds for the Urgent Low Glucose Alarm, if you don't want it to disturb sleep, are:
Turn off your Bluetooth before bed. The simplest solution.
Turn the app off completely on your phone
Turn off your phone
When using these methods the sensor will continue to store your glucose readings for a rolling 8 hours. So if you have the app not running for 10 hours you will loose the first 2 hours of data when you turned it off. For example if you turn off bluetooth at 10pm and do not turn it back on until 8am you will loose the glucose readings between 10pm and midnight.