Sir, I did as you mentioned, but nothing changed. When I gave Interior for partition line in named selection and imported to fluent, it created that named selection which I gave but along with part_2 which also represents the same partition lines.

And Sir I don't know how to put the selected boundary as interior because I cannot see any option like that In Boundary Conditions, you can also check, I have scrolled down to the bottom bar but no option like interior is found. Or is there any other method to define that?
Can you please help how to solve this?
Sorry for posting the same query in other section because I thought that only fluent related post will be solved in that section, that's why I later post the same query in the preprocessing section.
Is there any other options like delete the discussion which I created from my side?