Help with modification of the machine startup Gcode

Hello all

i have a slightly banana bed and have installed a tronxy glass bed on top of my old engineering bed for printing. My issue is that the nozzle cleaning area though available is now 3mm below the nozzle when it comes to the cleaning area. How do i force the nozzle to travel another 3mm in -z direction when cleaning ?

any help modifying the machine start code would be very appreciated

bump! please let me know if any other links can be helpful