Settings > Menu and Function Keys > Function Key for Shift

Function Key for Shift
Press the key to access the second key level for a few seconds.
In addition the status of the function is indicated by the corresponding LED.
Proceed as follows by assigning the function key:
Note: For further information about the general procedures when assigning function keys, see Function Keys.

COMfortel 1400 - Firmware V2.2 - COMfortel Set V3.16 - Advanced Information V07 02/2019