this may be late, but o well

it depends on what you duplicated, if nurbs surfaces, you have to use attach surfaces tool under "edit nurbs", but this is more complicated then it sounds, you'll need to understand NURBs surfaces before you begin attaching and detaching NURBs surfaces

if polygon surfaces you'll want to first combine the two objects by > selecting two or more polygon surfaces or objects > polygon > combine

after combining them, you'lll want to merge edges or vertexs together > select two or more vertexes close to each other that you want to become as "one" vertex > edit polygon > merge vertexes > and repeat the process to connect the rest

note: the "distance' option under the merge vertex option indicates a range of how far the vertexes can be apart to be able to merge together. experiment and you'll see what i mean