Mend (or immobilise?) the thing (3,2)

I believe the answer is:

fix it

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'immobilise? the thing' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'mend or' is the wordplay.
'mend' becomes 'fix' ('fix' can be a synonym of 'mend').
'or' becomes 'it' (I can't explain this - if you can you should give a lot more credence to this answer).
'fix'+'it'='FIX IT'

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I've seen this clue in the Evening Standard.

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