you're meant to set the units first in 3ds max then import your model on the main toolbar click on custom then units setup from here you can change the display and system units,
System and Display units
It is important to note the distinction between System and Display units. Display units only affect how geometry is displayed in the viewports. System units determine the actual scale of geometry. For example, if you import a DXF file (unitless) containing a 1 x 1 x 1 Box, 3ds Max could import the box’s dimensions in inches or miles, depending on the System unit. This can have a significant impact on your scene, which is why it's important always to set up the system unit before you import or create geometry.
https://knowledge.autodesk.com/support/3ds-max/learn-explore/caas/CloudHelp/cloudhelp/2019/ENU/3DSMa...
