How do I create the model signal data using my experimental signal data?

Hello, Here is my coding. I am using the system identification to create a model for the experimental data. They are actually the data for corn oil. I am using the ultrasound transducer to obtain the transmitted, received, and time of flight signal. From the excel files, my 1st row is transmitted signal, 2nd row is received signal, 3rd row is the time of flight signal, 4th row is the time domain data. However, when using the system identification Matlab, I couldn't get the best fits model whereas, I don't know how to create the model from the experimental data. Do take a look on the excel file and the coding. Thank you.

Run = xlsread ('Corn1.xlsx');
x1 = Run (:,1);
x2 = Run (:,2);
x3 = Run (:,3);
y = Run (:,4);
figure
ax1 = subplot(2,1,1);
hold on
plot (y,x1, 'r');
plot (y,x2, 'r');
plot (y,x3, 'r');
title ('Corn')
Escape = xlsread ('Corn2.xlsx');
k1 = Escape (:,1);
k2 = Escape (:,2);
k3 = Escape (:,3);
k4 = Escape (:,4);
ax2 = subplot(2,1,2);
hold on
plot (k4,k1, 'g');
plot (k4,k2, 'g');
plot (k4,k3, 'g');
title ('Corn2')