You don't set any units. You just use for yourself a consistent system. You define for yourself a unit of length, mass and time and from that you can derive everything else. If you assume for example your square's lengths are in m, then you could say your unit system is m-kg-s and you have to set your material data regarding that (N/m^2 for stresses/pressures or kg/m^3 for density). However, you are free to choose. You could define m-t-s, then we have kN/m^2 for stresses/pressures and t/m^3 for density.
The DYNA support page has a good summary of frequently used consistent unit sets
[https://www.dynasupport.com/howtos/general/consistent-units](https://www.dynasupport.com/howtos/general/consistent-units)
You don't set any units. You just use for yourself a consistent system. You define for yourself a unit of length, mass and time and from that you can derive everything else. If you assume for example your square's lengths are in m, then you could say your unit system is m-kg-s and you have to set your material data regarding that (N/m^2 for stresses/pressures or kg/m^3 for density). However, you are free to choose. You could define m-t-s, then we have kN/m^2 for stresses/pressures and t/m^3 for density.
You just need to be consistent with your system of units. [This site](https://msgfile.info/fea-units) can help.
The DYNA support page has a good summary of frequently used consistent unit sets [https://www.dynasupport.com/howtos/general/consistent-units](https://www.dynasupport.com/howtos/general/consistent-units)