How can I find out the part number for my LG Tromm? ?

We are having the LE error code come on, on our LG Tromm model# WM1832CW. I have read that in most cases it is the Hall sensor that needs to be replaced. I have 3 questions, How do I find the right part number for my model number (I don't know what year it is). The second question is, Who do I call to order the part? The 3rd question is can I replace it through the opening in the back of the machine or do I need to take the top off of the machine?