Adjustment in leg isn’t for upper garment (7)

I believe the answer is:

singlet

I'm a little stuck... Click here to teach me more about this clue!

'garment' is the definition.
(singlet is a kind of garment)

'adjustment in leg isn't for upper' is the wordplay.
'leg isn't' anagrams to 'SINGLET'.
However, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for singlet that I've seen before include "underclothing" , "Sleeveless shirt" , "garment worn by men" , "Sleeveless garment" , "Something to wear" .)

I've seen this clue in The Sun.

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