Go over again, bringing up horse (5)
I believe the answer is:
recap
'go over again' is the definition.
(I've seen this before)
'up horse' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'horse' becomes 'pacer' (a horse which paces).
'pacer' in reverse letter order is 'RECAP'.
'bringing' acts as a link.
(Other definitions for recap that I've seen before include "Caper (anag)" , "Provide summary" , "Go over things again" , "Summarise, run over" , "Go over the main points again, in short" .)