Engineers have couple to fix (6)
I believe the answer is:
repair
'fix' is the definition.
(to fix something is to repair it)
'engineers have couple' is the wordplay.
I cannot really understand how this works, but
'engineers' could be 're' (Royal Engineers) and 're' is found in the answer.
'couple' could be 'pair' (synonyms) and 'pair' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for repair that I've seen before include "Make one's way (to); fix" , "Travel or proceed toward some place" , "retire" , "Fix, mend" , "It may be effected by" .)