There are no rewrite rules - as in mod_rewrite - involved but only mod_remoteip’s configuration
https://httpd.apache.org/docs/2.4/mod/mod_remoteip.html
RemoteIPHeader CF-Connecting-IP
should do the trick
and you should also add
RemoteIPTrustedProxy 103.21.244.0/22 103.22.200.0/22 103.31.4.0/22 104.16.0.0/12 108.162.192.0/18 131.0.72.0/22 141.101.64.0/18 162.158.0.0/15 172.64.0.0/13 173.245.48.0/20 188.114.96.0/20 190.93.240.0/20 197.234.240.0/22 198.41.128.0/17