Rectification tweaked by trading two letters — there’s documentary confirmation (13)

I believe the answer is:

certification

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'confirmation' is the definition.
(certification is a kind of confirmation)

'rectification tweaked by trading two letters there's documentary' is the wordplay.
'rectification' anagrams to 'CERTIFICATION'.
However, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for certification that I've seen before include "legal document!" , "Process of allocating film ratings" .)

I've seen this clue in The Hindu.

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