One kilometer is the same as 1000 meters. So, the equation is
[tex] km = 1000 m [/tex].
This equation tells you that you have to multiply the number of meters by 1000, to get the number of kilometers.
Your question is the opposite, so we have to solve the forementioned expression for m:
[tex] km = 1000 m \implies m = \cfrac{1}{1000}\ km = 0.001\ km [/tex]
