I recieved a solution from Bambu to adjust Z steps / Z compensation
In the start G-Code you have to add the following
M290.2 Z(Value) M500
with Value being expected height/actual height.
So mine was expected height 20mm / Actual Height 19.9009 so a value of 1.00497967etc
I tested it out and it did compensate and brought my Z height of the test cube up to 20.0152
It will also work for X and Y as well using the same line of code but swap the axis from Z to the one requiring compensation.