Connecting Time Machine to NETGEAR NIGHTHAWK router to backup Mac

Time Machine is software on your Mac that is used to back up the data on the Mac to another hard drive.

You might be asking about a Time Capsule, which is hardware......a router with a built in hard drive that was designed to store backups from your Mac.

Please verify that you are asking about a Time Capsule before you proceed to the next steps.

If you are, the Time Capsule will need to be reset back to its default settings using a Hard Reset. This will not affect any of the data stored on the Time Capsule hard drive.

How to reset your AirPort base station - Apple Supportsupport.apple.com › en-us

Then connect an Ethernet cable......which must remain permanently connected.....from one of the 4 Ethernet ports on the Netgear router to the WAN "O" port on the Time Capsule

Then, set up the Time Capsule again so that it will pick up the correct settings that it needs from the Netgear router

https://manuals.info.apple.com/MANUALS/1000/MA1645/en_US/airport_time_capsule_80211ac_setup.pdf