Swiatek, losing one unexpectedly, makes minor adjustments (6)
I believe the answer is:
tweaks
'makes minor adjustments' is the definition.
(I've seen this in another clue)
'swiatek losing one unexpectedly' is the wordplay.
'losing' is a deletion indicator.
'one' becomes 'i' (Roman numeral).
'unexpectedly' indicates an anagram.
'swiatek' with 'i' taken away is 'swatek'.
'swatek' is an anagram of 'TWEAKS'.
(Other definitions for tweaks that I've seen before include "Pinches and twists, maybe a nose" , "Makes little adjustments" , "Pinches and twists sharply" , "Some fine tuning" , "Pinches and twists, perhaps nose" .)