take a variable to set the file name…use filename.Split(“_”), this will split the filename…then assign newfilename variable to CN_50570000_arr(2)_FB030030_arr(1).docx
then you can use MoveFile actiivty and change the filename in destination path property.
You can first get the folder name with -
var = Directory.GetDirectories() function
so if you have only 1 folder then you can take that foldername and then again split and take the 2nd argument value and process it further with workflow.