Lost signal while trying to update

> Model: A7000|Nighthawk AC1900 WiFi USB Adapter - USB 3.0

   Not a router.  Look for "Model" on the product label.  Firmware
version?

> Lost signal [...]

   What does that mean, in terms of actual observables?

> [...] while trying to update

   "trying" _how_?

> [...] don't know where to start [...]

   Describe what you did?  Describe what you see?

> [...] and failed

   Which kind of "failed"?

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

   If you have a flashing power indicator, then you may be a candidate
for the TFTP recovery scheme.  See, for example:

      https://community.netgear.com/t5/x/x/m-p/1622096#M102004