Fiancé wants me to try something on him

My fiancé just told me that he wants me to “eat him out” (if that’s the right words for it)? Like he wants me to do it to his ass bc when he did it to me, I enjoyed it so much and he wants to know the feeling. Has anyone done that? Is that even a thing? Lol

Please no judgement, I had just never heard of that on a guy before