Where you’ll find LA: North Dakota? Not true! (7)
I believe the answer is:
pretend
'not true' is the definition.
(pretend can mean make-believe or false)
I don't understand how the rest of the clue works.
(Other definitions for pretend that I've seen before include "Imaginary, make-believe" , "Dissemble" , "bluff" , "Suppose" , "keep up appearances" .)