F5 Rewrite i rule to a different URL

Yogeshwar, try the following irule. What's the version and model of your f5?

when HTTP_REQUEST {
if { ([string tolower [HTTP::host]] equals "xyz.mmm.com") }{
HTTP::header replace Host "abc.com"
 }
}
when HTTP_RESPONSE {
HTTP::header replace Host "xyz.mmm.com "
}