You need to have assigned the Default outgoing message before loading anything into the Send Queue ("send later"). Once they are in the queue, the only option is to Edit them, there. I have a list of outgoing messages I rotate throughout the year, so I set the Default, then automatically generate 84 invoices and they all have the Current Default in the queue.

You cannot edit the Provided initial Basic Message from Intuit. Make Your Own, then set it as Default.

From Income tracker, the one function you find there that is OverDue Invoices, that is not an outgoing message seen in Preferences for Send Forms. It cannot be accessed. This has been reported as a bug for Years.