1000 g = 1 kilog (10³⇒kilo)
so, [tex]\frac{1000 g}{m^{3} }=\frac{1 kg}{m^{3} }[/tex]
Since I don't have your values from your experiment, I'm assuming you have your mass values in g. Your teacher wants them in kg, so divide each value (g) by 1000 .
Then divide this mass (now in kg) by your volume in m³. This will make your density units kg/m³