see this above post.
You can Read all files exists into a directory by using Directory.GetFiles(FOLDER_PATH+“\INPUT",”.",SearchOption.AllDirectories)
By using this you can read excel… and pass those read values into a String and use set Text option.
In the UiPath SetText option will have input value… and you have to pass this captured string value into SetText option.
This SetText option selector should use Upload area attachment location where you need to enter file path to attach the file.
Hope my inputs are useful.