Book of Hebrews...you come to the throne of Grace boldly, nobody could enter the holy of holies without blood as an offering, but now Jesus has entered by his own blood. And so we can 'plead the blood' now because of Jesus giving his own blood. Thats how I understand it works.I think it's a made up doctrine, no where in the new testament is there any mention of this.
I also heard derek Prince teaching this I dont think he made it up, but just explained what was already in the bible better. Without shedding of blood there is no remission of sins. Because Jesus shed his blood, we can be forgiven.