This is a pdmod. You will need the Diesel Bundle Modder to install it.
https://modworkshop.net/mod/22724

Instructions (Instructions are for PAYDAY 2 but same steps apply, just choose the PAYDAY The Heist folder instead):
https://steamcommunity.com/app/218620/discussions/8/1735465524709205221/#c1735465524709616044