Welcome to the Community,
I'd recommend you take a look at the vSphere 5.1 Documentation Center to find out about how to setup Software iSCSI.
What you basically need to do is to remove the 2 NICs (vmnic2 and vmnic3) from the current vSwitch, create a new vSwitch with 2 VMKernel port groups and the two vmnics and configure the port groups to use one vmnic as active and the other as unused (i.e. port group 1 --> vmnic2=active, vmnic3=unused and port group 2 --> vmnic2=unused, vmnic3=active). Once this is done you can create the iSCSI adapter in "Storage Adapters" and add the two VMKernel ports.
It's also important to consult the storage vendors documentation. Storage vendors usually provide best practices guide for how to setup iSCSI on ESXi to work best with their hardware.
André