Forwarding unresolved DNS query by the configured zone

I have an F5 GTM answering authoritatively for example.com and sample.com. One more zone is configured for forwarding.com is to be forward zone with forwarders configuration to 2 external server. This is working fine till now.

 

On top of this, how can I configure where F5 will forward any other wildcard domain to another external server? Can I configure the wildcard zone in this case? Or is there any iRules required?