Need to mimic the edges/vertices of a mesh to the one in front to cause the cuts for then merging it

can someone tell me how to make faces in front of objective mesh… mirror them so I can merge them through removing dobles? (targeted take of my project)
I want the larger segment to break down into the one in front.

I don’t want the larger segment to change its shape just to have the cuts for merging with remove dobles. It doesn’t have to be exact I’ll adjust “merge distance” to 0.1 and that should be enough.