Nighthawk needs remote reboot

> [...] my Nighthawk router located at my winter home [...]

   Has it a model number?  Firmware version?  Connected to what?

> [..] requires a remote reboot. [...]

   "requires"?  You determined this how, exactly?

> [...] I have downloaded the Nighthawk app but have had no success in
> contacting the Nighthawk. [...]

   "no success" 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 would think I would need to supply network name and password
> for the Nighthawk [...]

   "network name"?  You'd certainly need some password, but there's more
than one.

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for "Types of Logins" and "remote".

> [...] which of course operates with a different internet service than
> the one at my summer residence. [...]

   I'd expect that to be the least of your troubles.

   For an explanation of why I believe that you're doomed, see:

      https://community.netgear.com/t5/x/x/m-p/2120209

   There seems to be a rash of these queries, lately.