How to select only 'wan' sub section in interface section in CBI

I need to modify some parameter of 'wan' sub section in interface section using CBI but I can't select wan section along. I only can select interface section. where LAN and WAN both available but I want only WAN. How can I do that ?
Please help.
Thanks in advance.

The third parameter in line 3 reads "interface 'wan'", isn't that yielding the right result/interface?

No dear , Its not working