Basic example should be something like this:
### Routemap Config ###
set routemap Peer-IN id 10 on
set routemap Peer-IN id 10 allow
set routemap Peer-IN id 10 match network 192.168.10.0/24 exact
set routemap Peer-IN id 20 on
set routemap Peer-IN id 20 restrict
### Apply For the Particular AS ###
set bgp external remote-as <AS-NUMBER> import-routemap Peer-IN preference 1 on
### Apply For a specific Peer ###
set bgp external remote-as <AS-NUMBER> peer <PEER-IP> import-routemap Peer-IN preference 1 on
### SAVE ###
save config
CCSM R77/R80/ELITE