How to replace the 02 Heater circuit (bank 2; sensor 2)?

A heater circuit code isn't a part, it's a code saying that there is a problem with the circuit that powers the heater inside the rear O2 sensor. Testing it isn't hard if you have a bidirectional scan tool. Without one it's a bit harder but requires only a piece of wire and a test light. You need to go under the truck and find the rear O2 sensor, it's at the back of the catalytic converter. There are two wires to look at, one is black and the other is dark green with a pink stripe. To test you need to go to the power distribution center under the hood. In there you will find the downstream O2 relay. If you remove it then go to the O2 sensor and disconnect it, connect a test light between the dark green and pink wire and the black wire. Now go back to the relay socket and jump the 30 and 87 terminals with a short wire, If the light comes on the circuit to the sensor's heater is okay. In that event it could be a bad sensor internally, to test that you can use a multimeter to test the resistance across the heater You just touch the probes to the heater connections at the sensors two pins (1 and 2 as in the image) that go to the heater You want to see what the resistance across the terminals is. Normally you will see between 10 and 20 ohms. If you see an open circuit or a very high resistance the heater is bad, and you need to replace the O2 sensor.

https://www.2carpros.com/articles/how-to-use-a-voltmeter
https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor