According to the RRC specification, cellSpecificKoffset is:
Scheduling offset used for the timing relationships that are modified for NTN (see TS 38.213 [13]).
The unit of the field K_offset is number of slots for a given subcarrier spacing of 15 kHz.
If the field is absent UE assumes value 0

This parameter `cellSpecificKoffset_r17` can be set in the gNB conf file, in the section `servingCellConfigCommon`