You didn't specify what model you have, but if you are looking at the Basic Wireless settings on the router. Try scrolling down the page. It will look similar to this:
You didn't specify what model you have...
And does it do 5GHz?
You would not be the first person to turn up here asking about 5 Ghz for something that does not support it.
Throw the desktop genie at it:
Do you see both vertical tabs?
My network DM200 -> R7800 -> GS316 -> PL1000 -> Orbi RBR40 -> Orbi RBS50Y -> RBS40V