Just replaced bank 2 sensor 2 on my pickup and today the engine light comes on a on 2004 Chevrolet Silverado 1500

nd says that the 02 sensor bank 1 sensor 1 needs to be replaced. Where is this sensor located please?

Drivers side front sensor. That is the answer to your question not your trouble code.
2 more answers , 3 more comments
agree with master tech only the circuit has issue not necess the sensor
code number never identifies a bad part just a failed system. get it checked to be sure.

trouble code says bank 1 running too lean
Check for vacuum leak on left (drivers side) of engine. Is eng. running ok.
Smooth idle?
Running fine.