Pizzanova, look for the dtb file in /boot/dtb/allwinner.
You will have to convert it to DTS (which is the editable device tree source) with dtc, using:
dtc -I dtb -O dts -o sun50i-h6-orangepi-3.dts sun50i-h6-orangepi-3.dtb
Then, edit the sun50i-h6-orangepi-3.dts and change it according to what you want to achieve.