I have check engine light on and the code reads po491. My friend said it could be either the secondary air injection pump or relay. So I got the cheaper part first the relay but I cannot figure out where the dam thing goes. Can somebody please help me fix my problem

Code reader says po491 which is secondary air injection system bank 1. Friend says it could be the relay and to try to replace that first. So i went and got the relay but now can't find where to put it. Can somebody tell me where it goes