How to damage one thousand plus 2 (6)

I believe the answer is:

impair

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

'how to damage' is the definition.
I can't judge whether this definition defines the answer.

'one thousand plus 2' is the wordplay.
'one thousand' becomes 'im' (I've seen this in other clues).
'plus' is a charade indicator (letters next to each other).
'2' becomes 'pair' (pair is a kind of 2).
'im'+'pair'='IMPAIR'

Can you help me to learn more?

(Other definitions for impair that I've seen before include "Hobble" , "Courteous man (colloq.)" , "blunt" , "Damage or injure" , "'Mar, damage (6)'" .)

I've seen this clue in the Sydney Morning Herald.

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