Due to the way the bender is constructed there should be no such offset and hence there is no adjustment pot for this.
Reasons could be a faulty bender pot, faulty opamp IC1 on the bender panel or a missing ground connection somewhere. Very hard to tell without access to the synth.
After the Juno-66 install you will be able to correct for this behaviour via the ‘pitch bend calibration’ procedure, but this is not a real fix however, rather a workaround..