Chart need a visual comand to find a series by title

[JASONW10]

I have a pivot table and everytime I change it the amount of series in my chart changes. However, I want to make a visual statement that will find the average series then increase its size of the line. line chart. Any ideas

 

[JASONW10]

If someone can tell me how to write a visual statement that will tell me the last line series in a chart; I think I can write a command to accomplish this.