Using RT-N66U as Local DNS server

hello everyone. I have been doing some research on a problem I have on my local home network. I need the use of a local DNS server to resolve some internal network names. installing a windows DNS server for this was not practical. I had read that when using ASUSWRT-Merlin you can accomplish this. But my research has yet to uncover the "how to" I have already loaded the firmware and looks and works great. What steps to I need to do in order to enable local DNS resolves and how to I enter them.

Thanks in advance for your time.