The Red Dot - S3-E12
Continuity mistake: After Elaine unwraps her cashmere sweater, Kramer wraps the ribbon around his neck in a scarf-like way and then lies back on The Couch. In a long shot of The Apartment (as Elaine exits the bathroom), the ribbon is gone, but when it cuts to Kramer and he asks about The Red Dot (and for the rest of the scene), the ribbon is back.
Answer: The name is Delores. He shouts that name at the end of the episode. Then in a later episode, "The Foundation", he runs into her. And he repeatedly calls her Delores.