Try this, and see this article on usage of the FFT to understand how to interpret the results and assign results to frequencies. Your time data does not make sense so I just plot results on a range of 1:n for frequency.
clc;close all
x1 = importdata('Plot-try-matlab-1.txt');
time = x1(:,1);
N = length(x1);
n = 2^nextpow2(N);
Y = fft(x1(:,2),n);
plot(1:n, abs(Y));
https://www.mathworks.com/help/matlab/math/fourier-transforms.html
https://www.mathworks.com/help/matlab/math/fourier-transforms.html