Max value from previous month in line chart as line per month

[#1]

Hello, I need help.

First, I want to show values per month in a line chart - no problem.

Second, I want to compare the values of month with values from previous month.

But in line chart the previous month max (min or avg)  values should be shown as line per month in the same area like values from first step.

How can I realize this complexe quest?

THX