Emergency brake not working after dealership serviced the rear brakes, how do I adjust the emergency brake myself?

I had my rear brakes serviced at the dealership and when I received my vehicle back the emergency brake was not working at all. I used my emergency brake all the time so I know it worked and being too busy to go back to the dealership to have them fix it I was without for a while. So, another shop was open on the weekend and looked at it for me and discovered it just needed to be adjusted. I now want to adjust it more so it will hold the truck on an incline and like I said I used it all the time before and I can tell by how hard it is to push the pedal down that it needs to be adjusted more. So, I just want to know how to adjust it, I don't want suggestions like take it back to whoever because I have my reasons for not taking it to anyone I want to adjust it myself and by the way the mechanic who adjusted it to where it is now it took a matter of 5 minutes, so I know I should be capable. Thanks so much for your expertise and most importantly your time in responding to my question. This 2015 e350 is a dually box truck Thank you.