Why do you change them? Did you get a post cat inneficiency code?
The post cat sensors should connect on the left side of the engine (driver's side) - opposite of the pre-cat sensors (mirrored, but on the other side of the engine).
You will need to have the car jacked up safely on stands, then once the old ones are out, you will need to fish the electrical cable & connector with a string or a wire. You might want to observe the original routing.