Change scale of axis values

Question

I created a distance matrix scatter plot of a series of points with genetic distance on the y-axis and geographic distance on the x-axis. The genetic distances range from 0 to 1. My geographic distances range from just a few meters to 5,000,000 meters. The resulting x axis values are in scientific notation (1e06, 2e06, etc.). I'm looking for a way to convert those scientific values to km instead of meters so that the axis reads 1000, 2000, etc.