have to say that I don't hook my exp pedal to the kemper (instead I hok them into my pedalboard)......given this, you should find the calibration thing right where you find the details of the pedal/switch 1 and 2 assignment.
it should be on the system menu................and as far as I remember it is not called calibration but initialization. anyways, check the manual first or the wiki: both covers virtually all the questions you might have.
uhm.........have a minute patience, my friend that someone more wise than me will help you for sure. this is a great community and things a lot worst than yours have been magically solved. trust me: in a matter of hours you will have your pedals alive and kicking......... 
passed two days ,, no one answers (((
Summer is sooo short in Berlin ... 
I for instance was recording accoustic guitar.
No Kemper last week...
The pedal range can be set in the RIG menue page 3 the second knob.
i don`t find any solutions on forum and manuals
It is in the reference manual page 21.
But don't let it confuse you, IMHO there is a typo: "When you turn “Volume Pedal Range” to the left half, the volume pedal turns from an attenuation pedal into a booster pedal." just makes no sense unless you read it as: "When you turn “Volume Pedal Range” to the right half, the volume pedal turns from an attenuation pedal into a booster pedal."
Anyway what you want to do, volume from -3/4 at heeldown until maximum at toedown should be somewhere around -3,5 or so.
"added: continuous pedal calibration " - in the latest beta firmware
I also never understood what exactly this means. I guess it means that the pedal calibration does not have to be done again after a reboot.
