I wanted to send 193.16.0.0 /19 Subent traffic to one member of the pool and rest to another pool member .

There are a few good resources for learning how to do iRules, including the iRules 101 articles and this wiki page that talks about checking ip addresses.

For what you would like to do, I'd suggest reading through the articles there to understand better how to write iRules, and then look into something like this (although if you're trying to manually set the backend node, I'd recommend making 2 pools, and setting the pool instead for those coming from that subnet instead of setting the node.

when CLIENT_ACCEPTED {
    if { [IP::addr [IP::client_addr] equals 193.16.0.0/19] } {
        node 1.1.1.1 80
        pool POOL_A
    } else {
        node 1.1.1.2 80
        pool POOL_B
    }
}