HELP

> I just purchased Netgear AC1750 router [...]

   "AC1750" is a speed, not a model number.  Look at the product label.

> [...] & very excited to connect it. [...]

   "connect it" to what, why?

> [...] My problem is my current Netgear router 7550 with AT&T as ISP.
> [...]

   That's a DSL modem+router.  Did you intend to replace the 7550
modem+router with the (still-a-mystery) "AC1750" router-only(?), or did
you intend to use the (still-a-mystery) "AC1750" router-only(?) to
extend your wireless-network coverage, or what?

> [...] They are clueless! [...]

   Pot?  Kettle?  ("HELP" was a Beatles movie; it's not a useful problem
summary.)

> [...] I can't connect to WiFi so I can connect new product. [...]

   "can't" is not a useful problem description.  It does not say what
you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

> [...] I have an ethernet connection [...]

   From what to what?

> [...] so I can use Nighthawk app. [...]

   You shouldn't need the "Nighthawk app" to configure your new
(still-a-mystery) "AC1750" router-only(?).  You should be able to do it
with a web browser.

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual.  Read.

> [...] I logged into Netgear router to check configuration. [...]

   How, exactly?  And what, exactly, did you do after that?

> [...] Ethernet-IPv4/IPv6 says "connected to internet,connected to
> unknown network" WiFi says "connected to unknown network, no traffic"
> IPv4&IPV6 Disconnected.

   I don't know what that means, or at what you might be looking.  I
also don't know how you connected your new (still-a-mystery) "AC1750"
router-only(?) to anything.