How do you change to 2.4 GH on a c7100v router.

[ddclayton]

I am installing a air purifier and instruments say I can not use 5 GHz,  How can I tell if I'm using 2.4 GHz.  Or how do I check to see if I'm using the right one?

[antinode]

> I am installing a air purifier [...]

   Thanks for the detailed description.

> [...] and instruments say I can not use 5 GHz, [...]

   "instruments"?  "instructions"?

> [...] How can I tell if I'm using 2.4 GHz. [...]

   That might depend on what your (unspecified) mobile device is.

   Possibly interesting:

      https://community.netgear.com/t5/x/x/m-p/2096739