Connect a second router

[TazR]

Here is my current state:

I am using my own Netgear router with FIOS. It is in my second floor and connected to a wall outlet using an ethernet cable. My first floor has the ONT box. My third floor receives weak signal which is why I would like to set up a second router (an old Belkin) on my third floor. My third floor also has a wall socket saying “Data”. Is it possible to connect my second router on the third floor to FIOS? If yes, could anyone please provide step-by-step details? 

[dslr595148]

#1 Yes, sure setup the second router to act as Hub/Switch/WAP.

See https://www.dslreports.com/faq/11233 and https://www.dslreports.com/faq/12506

#2 If you have any questions, please ask.

#3 Unknown where the wire from Data Jack from the third floor goes to.

Data Jack on third floor -> Data Jack on second floor OR Data Jack on first floor??

#4 Unknown if the Data Jack on the third floor is connected to anything or not.