Z axis/offset will not go below (0.00 mm) to and will not adjust

please help.
flashed the firmware for the 4.2.7 board on my ender 3 and when I try to lower the z axis to figure out the probe Z offset it will not allow me to move it beyond 0.00 to figure out the off set also if i use the probe offset option it will not go pass 0.00 and will not adjust so the nozzle stay up away from the bed.
I have tried reflashing the firmware a bunch of times changing the file name every time even resetting the eeprom and the same issue.
please help.

Did you try using the z-offset wizard under configuration?