To reconfirm, simply advise your airline by telephone or in person of your intention to use your return or continuing reservation.
All airlines require a minimum of two hours check-in time.
Go directly to your onward carrier and check-in. Your airfare is based on the itinerary as shown on your ticket. In the event that you change this routing, your airfare may also change. You must consult with the airline involved to determine your exact rate. The face value of the ticket you now hold, should be applied to any alteration of the itinerary.