What can be done if one date is wrong?
 

Our older son was making reservations, and he got the day of the flight wrong, flying from San Francisco to Maui on United. The reservation was made 3 days ago, so we are past free change within 24 hrs. The flights will be in August.

Can we change the date of flight for 1 leg only? How much it would be for 2 people? Will this involve refund and making a new reservation, or only the date change for 1 leg?

Any other options?

yes, you can change one leg only. Cost depends on a couple things - fare class and associated restrictions, availability of same fare class on the date you want, etc. Technically you are outside the 24 free cancellation window so will likley face a change fee which is per person, plus any change in fare per person.
I'd call UA and try the "my idiot son booked the incorrect date, what can be done?" approach in the hopes you get a sympathetic agent.

Junior is taking the trip; junior flubbed the date. So Junior should be on the phone trying to make amends, not his parents.
You mean well, of course (and may be paying the alteration fee), but this is also a lesson in self-sufficiency. Good luck, and good trip.

Thank you both! He is changing the date of the 1st leg, and paying for it :)

Another darn learning experience!

LOL