Represent first person up at organisation (6)
I believe the answer is:
embody
'represent' is the definition.
(I know that embody is a more specific form of represent)
'first person up at organisation' is the wordplay.
'first person' becomes 'me' (first-person pronoun).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'at' is a charade indicator (letters next to each other).
'organisation' becomes 'body' (body can mean an organisation or group).
'me' reversed gives 'em'.
'em'+'body'='EMBODY'
(Other definitions for embody that I've seen before include "Epitomise" , "Include (something) as a constituent part" , "Give solid form to" , "Stand for" , "Incorporate or express in visible form" .)