How can I find the plot lines in a figure with 3 plots?

the user gives the function a figure with 3 graphs ( 3 plots) in it. I want to change the line color and LineStyle of each one. How can I do it? I've tried findobj(gcf,'type','line') but for example in a figure with 3 graphs, it finds 16 line objects. How can I find out which ones are the graphs? Note that the user will give different figures to the function. so I cant not count the lines and try to find which number is for which line.