Knocked to the left in garret, lamp switch (5)
I believe the answer is:
alter
'knocked to the' is the definition.
I can't judge whether this defines the answer.
'left in garret lamp switch' is the wordplay.
'left' shows that the letters should be reversed in order.
'in' indicates the answer is hidden within the clue.
'retla' is hidden in the letters of 'garret lamp switch'.
'retla' written backwards gives 'ALTER'.
Can you help me to learn more?
(Other definitions for alter that I've seen before include "Alert to change" , "convert" , "Bout of extravagant spending" , "Change, make different" , "shift" .)