I'm not sure about abaqus, but in ansys workbench there is an option in contact setting dropdown to give conductance value as a curve or number

you should use User subroutine GAPCON. reffer to Manual.

Manual definition:

++++++++++++++++++++++++++

+++++++++++++++++++++++++

SUBROUTINE GAPCON(AK,D,FLOWM,TEMP,PREDEF,TIME,CINAME,SLNAME,

1 MSNAME,COORDS,NOEL,NODE,NPRED,KSTEP,KINC)

C

INCLUDE 'ABA_PARAM.INC'

C

CHARACTER*80 CINAME,SLNAME,MSNAME

C

DIMENSION AK(5),D(2), FLOWM(2), TEMP(2), PREDEF(2,*),

1 TIME(2), COORDS(3)

user coding to define AK(1) -- AK(5)

RETURN

END