i have an upcoming round trip booked on UA. I need to cancel the first leg as my plans have changed and I am arriving from a different city on another carrier.
I definitely want to keep my return flight.
I tried to do this with the UA mobile app but there is no way to cancel just one leg— only the whole transaction.

And i I do not want to cancel the whole thing and rebook only one leg this close in due to the upcharge and change fee.

Nor do I want to just no-show the first leg because I’m pretty sure they would then cancel the return flight.

So, how can I do this?

Thanks!