Hi, what are you trying to do?
I don't think there is one by default.
If you're using native plugin from FL (harmor, sytrus) there are a bunch of effects that are available in the piano roll.
Like Slide, portamento, notes, color notes that trigger effects.
If you left click on any button in a plugin you get a list of different automation available.
For everything non FL, it depends of the plugin, but you can use various type of automations.
Left click wont work usually.
You can either use "browse parameter" from the plugin window(click the down arrow top left), then a list of everything you can automate (parameters, CC) will popup.
Usually "midi CC #1" is used by modwheel.
From there you can use "edit event" to draw curve in piano roll , "create automation curve" to draw clean spline-curves in the Playlist, or "link to controller", for example "dashboard" plugin.
I used it to create a sustain pedal for a bass.
You have fruity keyboard controller to control a parameter from the piano roll depending of the note, or the velocity of the note.
There is another method where you move any parameter in the VST window (like modwheel), then go to tool, last tweaked parameter and you get the same automation menu. But it doesn't work 100%