This blacksmith is the younger brother of Delvin of the Thieves Guild in Rift Valley City. If you have completed the main quest "Clearness" of the Thieves Guild before meeting him, then a dialogue will be triggered and he will ask you Help him find someone who stole his bone armor formula. After receiving the mission, it is easy to find it according to the instructions. It is in the lair of a snow goblin, as soon as you enter the cave entrance.