How to enter two dynamic variables for two selected date ranges

I am trying to create a what-if scenario to see what happens when I add two sales amounts for two different date ranges.

I have a sample report attached to this report.

For example, I have a total sales of 1000 dollars for all months.

Now I want to see the variation for each month by adding two variables for two date ranges as shown below. 

I have uploaded the link to my OneDrive of sample report. 

https://1drv.ms/u/s!Ah7Jz5diWiAHgogU5mp3MgFDBsqI6Q?e=HLX4HW 

I would highly appreciate your support.