reusability or trash can?

> [...] it's predecessor: N600. [...]

   "its".  "N600" is a speed, not a model number.  Look for "Model" on
the product label.  Firmware version?

> [...] find new purposes as extenders?? [...]

   Define "extenders".

> Model: R7000|AC1900 Smart WIFI Router

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual.  Look for "Set Up the
Router as a WiFi Access Point".  Repeat for a similar topic in the
"N600" docs, whatever it is.  A sufficiently old model might not have a
convinient WAP mode option, but practically any model can do it.  See,
for example:

      https://community.netgear.com/t5/x/x/m-p/1463500

That's written for a Netgear C6300-as-WAP, but the steps are about the
same for any other router (any make/model) which lacks a one-step WAP
option.

   If you had something else in mind, then further reading might be
helpful.