Royal Engineers with shop to repair (7)
I believe the answer is:
restore
'repair' is the definition.
('restore' can be a synonym of 'repair')
'royal engineers with shop' is the wordplay.
'royal engineers' becomes 're'.
'with' is a charade indicator (letters next to each other).
'shop' becomes 'store' ('store' can be a synonym of 'shop'**).
're'+'store'='RESTORE'
'to' is the link.
(Other definitions for restore that I've seen before include "Give back - return to former state" , "hand it back?" , "Strengthen" , "Cure" , "Repair, put back" .)