getline function not working in RHYTHM 2.0 GUI

Hello all, I am currently testing out the conduction velocity function of an opensourse GUI written using MATLAB (https://github.com/optocardiography/Rhythm-1.2/blob/master/README.md) and noticed that the following functionality is not working as intended (copy and pasted from the README):

If you want to calculate CV along one direction (e.g. longitudinal or transverse CV), you should click “Draw Line”. Then you should left-click on the starting point of the direction of interest, right-click on the ending point afterwards. “Calculate CV” calculates average CV in a rectangle within 5 pixels of the line and with CV direction within 15° of the selected line direction. Five numbers are printed in Statistics panel. These are median conduction velocity, mean conduction velocity, standard deviation of the CV, the total number of vectors included in calculation and mean vector angle.

I cannot click and drag a line out in the first place. Can anyone please assist me with this? Thank you.