archer 1600v router: sharing router connection via cat6 cable then back to Wi-Fi signal

> [...] I have a Supplied archer v1600 TPlink, router sharing coms.

   Huh?

> [...] I've tried older modems like a N300 and N600. [...]

   "N300" or "N600" is a speed, not a model number.  Look for "Model"
on the product label.

> Model: D3600|N600 WiFi Modem Router - 802.11n Dual Band Gigabit

   Is "D3600" one of your actual model numbers?

> [...] But none seem to work what ever setting I try.

   Think, for a moment, about how little useful information that
(non-)description conveys to the non-psychics in your audience.

> [...] convert incoming Cat6 cable back to Wi-Fi [...]

   You might want to configure one of your old routers as a wireless
access point.

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual.  Look for a topic like
"Set Up the Router as a WiFi Access Point".  Not all models have a
convenient option for this, but practically any model can fo 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.