You x-axis exponent has me believe that you already have the correct range and that your goal is to show nanoseconds instead of seconds on your x-axis (note the 10^-8 at the end of your axis).
You can do this two ways: either change the data, or change the axis ticks. The first is easier, but I chose to do the second.
plotData = importdata('nosnoise.csv')
plotData.colheaders(1)
plotData.data(1)
figure(1)
clf
hold on
grid minor
plot(plotData.data(:,1),plotData.data(:,2),'x-m')
plot(plotData.data(:,3),plotData.data(:,4),'x-m')
title('ESD event for the CDM')
x=linspace(0,20,5);
set(gca,'XTick',x*10^-9)
set(gca,'XTickLabels',cellfun(@num2str,num2cell(x),'UniformOutput',0))
xlabel('Time (ns)')
ylabel('Voltage (V)')
legend({'Immunity to power supply noise'})
