How is the narrative technique in this section different from the rest of the novel?

The narrative is no longer a first person limited omniscient view from Offred. Instead it involves a detached speaker lecturing about the merits or lack of merits of Offred's story. The sanitized and very academic ending is in stark contrast to the very gritty personal account of Offred's journey.

Are you taking about the epilogue here?

The epilogue is a symposium, we have a 'guest speaker,' who takes over for Offred in the telling of a 'tale.' The speaker, who tells the story through historical notes reveals what Offred couldn't.