Change colour of KPI (count of cases) compared to previous week/month

The problem is i need to put a field holding last months data in “Value”, rather than a number i enter. Is there another way to compare the current months data to last months data? I have seen a couple things where they use other filters but i do not understand the process of doing it.

For example - Comparison with previous month while displaying all data for a month on Quicksight

Although it does not change the colour, i have a clear comparison of data from two different months