Hi 5 years later :)
I just figured this out and thought I'd share it since i ran into the same issue.
Download software
Go to https://line6.com/software/index.html
-Choose Software- select Line 6 FBV Control
(for some reason the search sometimes doesn't work, i had to find it using different search filters, aka choose hardware FBV Express MkII and not select an operating system)
Install + Run Line 6 FBV Control
Set the "Midi Command" of all controls to "MIDI CC" (some controls like the "Pedal Wah" will already have this assigned)
All the controllers you changed to "MIDI CC" change the value to something that's not already selected by another control
If you want you can change the Switch mode from Toggle to Momentary
Start Presonus Studio One (I'm using v5.4.1)
Adding External Device
Go to Options --> External Devices --> Add..
New Control Surface
Manufacturer: "Line 6"
Device Name: "FBV MkII Express"
Receive From: FBV Express MK II
Send To: None
Set Up
On your "Mix" panel (not Edit or Browse) select "External" and you should see "External Devices" pop up with the FBV MkII Express
Right Click on FBV MKII Express --> Edit...
Click MIDI Learn
Push all the 4 Buttons + Move the Pedal + Hit the Toe Switch (very hard press on the toe of the pedal)
Link to VST
On the top left of Studio One, whenever you push something on your pedal you should now see "Control 1" getting updated
Move a knob on your VST or in Studio One interface and you should see the left side of "Control 1" changing. Now just press the little left arrow/triangle between the two and you have a controller set-up
Link to Pod Farm
Using Pod Farm VST needs an extra step. Create a track then add your Pod Farm VST and open the vst interface
You'll notice when you move a Pod Farm knob nothing will change on the Notifier label next to "Control1."
Right Click on the knob you want to change in your Pod Farm vst and select Automation --> Knob 1
Now move the knob and it will again show up next to the "Control1" thing