Good deal. You should be snooping all over that radio. There's many things that aren't mentioned in any manual. There's long-running threads on RCG for many specific Spektrum components, including the DX family of radios. It's frequented by many experienced users, designers, engineers, etc.. alot of experience in that thread. I suggest jumping in and subscribing, and following it, and/or posting up in it if you have any more questions. It's easy to find.
They're doing many things with these DX radios, and they can't write any manual that's big enough..hence the ongoing threads seem to serve as a perpetual evolving source of info. Fortunately your problem here was very easy, but if you need complex advice, that's where you might want to look. Good luck with your radio.