How do I Waveform,FFT that data?

I want to display the file as Waveform, FFT.(The attached file)

But I think my coding has a problem.

Can you look at it? I want to set the frequency in MHz

clear all; close all; clc;

[filename directory_name] = uigetfile('*.dat', 'Select a file');

fullname = fullfile(directory_name, filename);

data = load(fullname);

t = data(:,1)*1e-3; % Convert To‘seconds’ From ‘milliseconds’

v = data(:,2); % Voltage

L = length(t);

Ts = mean(diff(t)); % Sampling Interval (sec)

Fs = (1/Ts)*1e6; % Sampling Frequency

Fn = Fs/2; % Nyquist Frequency

vc = v - mean(v); % Subtract Mean (‘0 Hz’) Component

FTv = fft(vc, L*4)/L; % Fourier Transform

Fv = linspace(0, 1, fix(length(FTv)/2)+1)*Fn; % Frequency Vector (Hz)

Iv = 1:length(Fv); % Index Vector

subplot(2,1,1);

plot(t,v);

title('Waveform');

xlabel('Time domain[ms]');

ylabel('Amplitude[mV]');

grid on;

subplot(2,1,2);

plot(Fv, abs(FTv(Iv))*2)

title('Spectrum');

xlabel('Frequency[MHz]');

ylabel('Magnitude[dB]');

grid on;

[Walter Roberson]

What is the difference between this question and https://www.mathworks.com/matlabcentral/answers/399456-i-want-to-display-the-attachment-as-waveform-fft ?

[Ameer Hamza]

The first column of your data does not seem to represent time. It contains negative values. Also, the time samples are very close, what is the sampling frequency of the signal.

[milksba]

I also checked the time frame is negative.

Fs = (1 / Ts) ; I did this.

No other sampling frequency has been set.

I followed the Internet.

[Ameer Hamza]

Yes, but how come the time is negative. Also, sampling frequency seems to be very large (in GHz). How can you display it in MHz.