Reveals unintentionally that one does tailoring alterations (4,3)
I believe the answer is:
'reveals' is the definition.
('let out' can be a synonym of 'reveal')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for lets out that I've seen before include "Reveals" , "rents" , "Discloses" .)