Netgear Orbi rbk50

You will need a  modem no matter what...  You currently have a modem/router combination.

Here are two options for you.

1.  Call your ISP and ask them if they can swap that modem/router for just a modem since you have your own wireless solution.

This is easiest and least cluttered approach.  Orbi would plug into back of modem without any fuss

2.  If they say NO, then your next best -- and cleanest -- option is to put their router into what is known as bridge (or passthrough) mode.  This turns off all router and wifi functions and lets your router (Orbi) do all those functions.

Here is the centurylink page to put it into bridge mode.  You want transparent bridging.  They say in here you still have to call them.

https://www.centurylink.com/home/help/internet/modems-and-routers/zyxel-c2100z/access-advanced-setup/wan-settings.html

Recommend you give them a quick call and see if they can swap.  If not, tell them you want to bridge -- also let us know and we can help with the Orbi side.

Here is your product sheet:

https://www.centurylink.com/asset/home/help/downloads/internet/c2100z-datasheet.pdf