The anode rod is located within the hot water discharge fitting on the tank. It sure would have nice for BW to locate a separate port for the rod!
Turn off the cold water inlet, open a hot water faucet, remove the hot water outlet-union and anode coupling. What you will be left with is a 3/4″ NPT port directly into the top of the tank.
Replace anode using plumbers sealant on all pipe fittings, and reinstall discharge line.