Setting up C7000 wirelessly as a repeater or Bridge?

Hello,

I had been using Nighthawk C7000 as my Cable/Modem prior to moving. Once i moved i had to switch Internet Provider to ATT, and they gave me their own Cable/Modem and told me i had to use theirs, which is fine but I get really slow speeds on the second floor, I was wondering if i could use my C7000 upstairs as a wireless repeater or bridge because i need the ethernet ports from the router for PC & PS4 and better coverage of my wifi upstairs. I can't wire a long ethernet cable from downstairs to upstairs, that's why I need to do it wirelessly. I looked at videos and guides all day and tried everything, im so exhausted. I called ATT, I called Netgear, both told me I had to sign up for warranty or pay for some monthly service lol....really?

I saw some guides are saying press the "Enable wireless repeating function" I literally don't even have that button, i clicked everywhere on the routerlogin page.

I know i can buy a Powerline adapter but i spent like $250 dollars on the Nighthawk and i really don't want it to lay in waste.

Please help me,

Thanks