SOPHOS FIREWALL PUBLIC IP 1:1 NAT Configuration

I HAVE A SOPHOS FIREWALL ALREADY CONFIGURED AND ONE INTERNAL SERVER ALREADY RUNNING 1:1 NAT MEANS MY EXTERNAL PUBLIC IP LIKE 1.2.3.4 ON PORT 2 AND INTERNAL MAPING IP 192.168.40.40 IN PORT 3 DMZ PORT.

NOW I HAVE OTHER COMPANY PUBLIC IP LIKE 5.6.7.8 WANT TO SAMECONFIGUR.ATION LIKE ABOVE 1:1 NAT. LIKE 5.6.7.8 MAPING IP 192 .168.20.20

ALL WORK WILL DO VIA TREAMVIEWER OR OTHE REMOTE DESK