Scenario analysis on sales data for several countries

Hi, I am new to PowerBI with a big project and a tight deadline, so any help would be greatly appreciated.

I have a table that has two columns. I call it "Country Data" and it looks like this:

Country Name          Sales Data

"Sales Data" has information per country name and a total for all countries at the bottom.

I need to develop a slicer (?) that should enable me to stress the sales data of each country individually to see the impact that it will have on the total. The stress can be the same or different for several countries (such as EU countries, etc), so that I can decide which stress to apply to which country. I would guess that I need to have a second table in which I will enter the same list of country names in one column, my potential stress levels in percent of the total "Sales Data" in the second column and a third column with the result (stress level * sales data)? The problem is that I don't know how to tell PowerBI to do that? 

As I said, any help will be greatly appreciated!

Thank you