My colleague called UA to change the flight. The same message remains. I have his reservation on my App.

Due to a prior schedule change impacting your trip, you have the option to make a one-time change to your flight(s) at no cost, or cancel and request a refund.

Your new flight must meet these conditions:
• Your new travel date is not more than 1 day before or 1 day after the original date
• Your origin and destination airports remain the same
• Your new ticket is in the same cabin and booking class as the original ticket
• Your new flight is operated by United and United Express
To make a one-time change, select "Change flights" below. To review cancel and refund options, select "Cancel options".