FT847 Gpredict, Radio Control

Hi everybody,
I am new here and on Gpredict also.
Have: raspi-buster, Gpredict, momemade CAT cable (it works fine), FT-847, yagi
after sucsessfully setup the rigctld (was not that easy) I have the following problem:
The doppler shift is corrected by Gpredict on main- and sub-VFO.
unfortunately is the frequ. not so transeive as it should be, especially in SSB.
when I turn the SUB-TUNE knob to correct, it is in the next moment overruled by Gpredict.
Same issue with the CLAR knob.
Does anybody have an idea how to cope with this issue ??
Is there a possibility to shift the VFO-frequ. permanently a little bit ( 1-3kHz) ??
Thanks for answer, 73, Karl OE3JAG