Hi Alvaro,
Ultimately to change the default DTB at the build level, you need to patch the UBoot recipe. You can see an example of how do that here.
As for the UART, the Ivy board does not have a UART console populated. My colleague @bruno.tx shows the details in this ticket. I’m working internally to see if we can get this info onto our developer site and maybe into the datasheet so others can find it easily.
Drew