2003 Subaru Baja reset check engine light

2003 Subaru Baja

How do I reset the check engine light on this car? It came on due to an O2 sensor (rear one 2nd in line) which a friend of mine just replace successfully last night. But how do we reset the light? Manual has no instructions.

For grins I tried disconnecting the battery but the light came back on at reconnection.

Sure appreciate any advice.