My family memberhas a upcoming round trip international flight.
NRT-SFO-DEN / DEN-SFO-NRT on L fare

My family member found out NRT-SFO / SFO-NRT is available on S fare

The price of NRT-SFO-DEN / DEN-SFO-NRT (L fare) is higher than NRT-SFO / SFO-NRT (S fare) + SFO-DEN / DEN-SFO (L fare).

He wants to change the ticket online. However, he can not change outbound and return at the same time. Only change outbound or return at a time.

It looks like cancelling and rebooking is not an option since there is a cancellation charge on his ticket.

Is there any method to change outbound and return at the same time online?

Thank you.