Measure before dabbling!

Either you have the source code for your current firmware, or you look it up via the settings you will find in the display controller. There will be an item which defines the steps/mm for the z-axis.

Now do the measurement with the calieprs as I posted before. When you go from z=0 to z=100 mm, the firware will move the stepper moter 100 times this steps/mm value. For example if the firmware thinks it is 100 steps/mm, it will move the stepper 100*100 =10000 steps to achieve the move.

So you now know how many steps were made by the firmware, and you have measured the actual movement in mm with the calipers. Now divide the (100mm*current_steps_mm, 100*100=10000 in this example) steps by this measured value and you have the actual steps/mm you need for the z-axis.

If you design and print a 150*150*1 mm square and print this you can do the same for the x- and y-axis axis by measuring

Be aware that in the source codes, there are multiple definitions for many printers. You will need to follow the logic for the defines starting from a file called configuration.h or similar.