Crespo Abyss S Rank Dungeon HELP

I would like to have someone explain to me a detailed guide to completing the dungeon "the man who is after the remnants quest" in the Abyss of Crespo. I have tried many times but when i kill protecters shield which is a skeleton dragon it just keeps reappearing and i never get to finish the dungeon.

PLEASE explain me how to complete the dungeon in detail. Thank You.