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Ok, This is referring to one of the O2 sensors. You have 2. The one in front of the catalytic converter is Bank 1 Sensor 1 and the one after the converter is the Bank 1 Sensor 2 Oxygen sensor. Stuck lean means that it is not reading properly and stuck reading a lean condition in the air/fuel ratio.
This is easy to replace. Crawl underneath vehicle and disconnect the O2 sensor connector and use either a special O2 socket(about $20) to remove, or a 7/8" wrench to loosen and remove O2 sensor from exhaust pipe.
Bank1 Sensor2 highlighted in yellow below: