Setup an old wndr 3700 router as an access point

I have a nighthawk R8000 router as my main router. I want to setup my old Netgear wndr 3700 router as a wireless access point.  Can someone tell me how to do this? I searched the internet and all the suggestions do not work.  My R8000  is upstairs and I want to increase my wireless connection  downstairs and  in the backyard.

I have 2 security cameras in the backyard and they are getting a weak wireless signal.   I currently have a Netgear x6s range extender downstairs but it is not giving me the added wireless signal I need. I thought the access point  might be a better solution.

Thanks,

Mike