Turn pale in sub-office when moving right to left (6)

I believe the answer is:

blanch

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'turn pale' is the definition.
(synonyms)

I don't understand how the rest of the clue works.

(Other definitions for blanch that I've seen before include "Become white or pale, maybe with fright" , "woman" , "Become like 17 Across, perhaps through fright" , "(Of vegetables) cook briefly in boiling water" , "Remove the colour from something" .)

I've seen this clue in The Irish Times.

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