So, how does your script provide the date?

Do you have a subroutine previous_day() somewhere that you call?

Please note that you have not reduced your original code, but started with some other code. Your problem seems to be how to integrate the code above with the code you have.

The first step is to reduce (and understand) the code you have to something manageable. The second step then is to integrate the new code to get the previous day.

While you have the parts to perform the second step, you haven't done the first step. The first step must be done before the second step.