What is the right way to handle this:

I was originally booked on a flight departing at 7:20 am. I wanted to go on a later flight departing at 1:05pm. So, using the phone app, I was offered and selected standby on the 1:05pm flight. I was quite sure that I would be successful, given the number of seats available so I didn't go to the airport for the 7:20 am flight. At 7:10 am, I got a call from the gate agent asking me if I'd be boarding. I told them no and that I'd be going standby later. I truly appreciated the call.

My question: Is there a better way to skip the original flight than simply just not showing up, so that Delta gate agents don't need to worry about me not boarding the original flight?

A second thing to note, is that the basic economy passengers are listed on the standby list, awaiting seat assignments. Those passengers are not really standby, and will take up many of the seats that are shown as available. So, it's important to take that into account so as not to get shut out on standby.