> RAX120 [...]

RAX120[v1] or RAX120v2? Look for "Model" on the product label.
Firmware version?

> [...] Does resetting it to default take the firmware version back
> down? [...]

No, but you should be able to do that, if you want.

Visit http://netgear.com/support , put in your (actual) model number,
and look for Downloads. (For older versions, under Firmware and
Software Downloads, look for "View Previous Versions".) Find the
kit(s). Download the kit(s) you want. Read the "Release Notes" file
for instructions. (In the User Manual, look for "firmware", and,
especially, for a topic like "Manually Upload Firmware to the Router".)
When that fails because of a deficient User Manual, try:

https://kb.netgear.com/23960

> [...] The fiber modem is a Alcatel-Lucent i-240g-c [...]

So, not really a "modem"?

Things generally work better with one router, not more. If you can't
disable the router functions of that (not-really-a-)"modem", then you
might want to configure the RAX120 as a wireless access point.

Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation. Get the User Manual (at least). Read.
Look for "Set up the router as a WiFi access point".

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Router Device List