How to find the tangent point of a fit curve that passes through a non tangent point?

Hi everyone,

I have curve that fit to data read from .xlsx file. How can I determine the tangent line as the picture below?

The number of the points is 100, so please see the xslx attached file.

Thank you.

My code:

    clc
    clear all
    close all
    filepath='c:\point for spline.xlsx';
    data=xlsread(filepath,1,'a1:b99')
    A_coor=data(1,:)

    % --- CURVE FITTING --- %
    f=fit(data(:,1),data(:,2),'pchip')

    % --- PLOT THE CURVE AND POINT A --- %
    plot(data(:,1),data(:,2),A_coor(1),A_coor(2),'ro')