Insert ad to shift items for part exchange? (5-3)

'shift items for part exchange?' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'insert ad' is the wordplay.
I cannot quite see how this works, but
'ad' is within the answer.
an anagram of 'insert' is 'treins' which is within the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...

'to' acts as a link.

Can you help me to learn more?