Phase Lag from CSV

So I have been reading a lot of these posts and doing my best but really struggling to figure this out.

I have a sixteen .csv files with time, input voltage, and output voltage all for different frequencies that I am trying to find the input amplitude, output amplitude, and phase lag for.

I imagine that I should be using fft but don't know much about how to do that. I attached one of the .csv files. Any help would be appreciated!