http header chnage when it redirects to https

If I understand you correctly, you'd like to change the redirect from https://test1.myapp.com to https://prod.myapp.com

This can be done with an LTM traffic policy, you can also use the following iRule.

when HTTP_RESPONSE {   
   if {([HTTP::is_redirect]) && ([string tolower [HTTP::header Location]] contains "test1.myapp.com")} {   
     HTTP::header replace Location [string map -nocase {"test1.myapp.com" "prod.myapp.com"} [HTTP::header Location]]    
  }   
}