how to fit a curve with the given trend to the limited data points

Please find the attached.

I have plotted curve 2 with the limited data point and want to continue it up to the horizontal axis like curve 1. Therefore I used curve fitting. The trends of the curve 2 should be the same as curve 1 however, after fitting a curve (dashed line), it shows totally different behavior after endpoint of curve 2. please let me know how to continue fitting curve trend similar to curve 1. here is whatever I have written so far:

x1= linspace(min(Mu_s_srt1),10,200);
p=polyfit(Mu_s_srt1,(1-Mu_s_P1),2);
f1=polyval(p,x1);
hold on;
loglog(x1,f1,'--k','linewidth',2);
hold on;    
loglog(Mu_s_srt1, 1-Mu_s_P1,'-b', 'linewidth',2);
grid minor;
hold on;

[dpb]

Attach the data and the equation for the target curve...

[Mos_bad]

Here are the codes and data. There is no specific equation. I just used CDF for plotting the curves.

[Mos_bad]

If there is any way to do that except CDF, please let me know.

[Image Analyst]

There is an assumed equation. You're using polyfit() to fit the data to a quadratic. Perhaps you want to fit the log of the data to a quadratic rather than the original data.

[Mos_bad]

Honestly, I do not have any preference. That was what I knew to do. The point is I need to write a code to plot the dashed curve such that follows the red curve's trend. However, as you can see it shows different behavior due to lack of data.

[Image Analyst]

It's hard to force the curve down on the right side when you're extrapolating. If you don't have a point out there to help pull it down, and just go by what you have on the left, it might not go down there. How about if you just specify one point way out on the right to help pull it down. It doesn't have to be that accurate, just something to help pull the extrapolation downwards.

[Mos_bad]

That's correct, no need to be that accurate, just follow the red curve trend. You mean just adding some data points manually?