Irule to redirect the traffic to UAt app on PROD server

Pretty straight forward to do in an iRule:

when HTTP_REQUEST {
    switch [string tolower [HTTP::host]] {
        "www.abc.com" {
            pool abc_pool
        }
        "uat.abc.com" {
            pool uat_pool
        }
        default {
            pool abc_pool
        }
    }
}

You can also do this without iRules with an LTM policy configuration. In either case you'll also want a OneConnect profile applied to the VIP: specific OneConnect profile + OneConnect enabled in the HTTP profile.