[find function nome operating by cockpit.]

hello everyone, i need help in assigning "buttons & switches" of FSUPC7 for MSFS2020.
I know how to assign a function to a key on a peripheral.
But how do I, in the case of specific functions of an aircraft know what that command is called in the list available in the "Button&switches" page?

For example, for the MB339, to start the engine you have to operate the switch "JPT LMTR", which obviously in the drop-down menu of available commands to assign is not there. surely there is but it is called something else.... 
is it possible to operate the switch from the cockpit, and detect the command name?