File assembled about iron tower's designer (6)
'tower's designer' is the definition.
'eiffel' can be an answer for 'designer' (I have seen 'French designer' mean 'eiffel' so perhaps 'designer' could also mean 'eiffel'). I am unsure of the 'tower's' bit.
'file assembled about iron' is the wordplay.
'assembled' indicates an anagram.
'about' indicates putting letters inside.
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'file' with letters rearranged gives 'eifl'.
'eifl' enclosing 'fe' is 'EIFFEL'.
Can you help me to learn more?
(Other definitions for eiffel that I've seen before include "French designer", "French structural engineer", "& 20 Across Paris landmark", "Parisian tower designer", "Famous tourist tower in Paris".)