5G connects to all but Ring doorbell- steps to simultaneously run Ring on 2G

> Model: C6300|AC1750 Cable Modem Router Docsis 3.0

   C6300[v1] or C6300v2?  Look for "Model" on the product label.

> Do not understand how to seup router for 2G and 5G simultaneously.
> [...]

   Switch on the power?  As with most dual-band routers, you'd need to
work at it to disable either the 2.4GHz or the 5GHz radio.

> [...] Checked manual - no answers. [...]

   Which "manual"?  Which questions?

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for a topic like "Specify Basic WiFi Settings".

   General advice: You might have more success if you described the
actual problem which you are trying to solve, rather than asking how to
implement some particular "solution" ("seup router for 2G and 5G
simultaneously"), which may have little or nothing to do with the actual
problem (whatever it might be).