Engineer with brace providing fix (6)
I believe the answer is:
repair
'fix' is the definition.
(to fix something is to repair it)
'engineer with brace' is the wordplay.
'engineer' becomes 're' (Royal Engineer).
'with' means one lot of letters go next to another.
'brace' becomes 'pair' (a brace is a pair of something).
're'+'pair'='REPAIR'
'providing' is the link.
(Other definitions for repair that I've seen before include "Correct" , "Make one's way (to); fix" , "Restore; go" , "Once, return" , "darn?" .)