I have a button box with rotary encoders ,I have one button when set to on is for VS, When set to off i have FLC enabled + i also use 2 rotarys 1 for climbrate VS and One for airspeed FLC.
The event your looking for is VS=AP_VS_ON
FLC=FLIGHT_LEVEL_CHANGE
Alternatively you could try this link which lists all commands [Event IDs] https://docs.microsoft.com/en-us/previous-versions/microsoft-esp/cc526980(v=msdn.10)