Ok, get the files from here: https://mega.nz/folder/oSESxDTJ#9U3_TGFAGGW_8ep9z_aCKw
I wrote the .img to an SDcard and then followed the instructions for the .dtb file.
The SDcard has two partitions, inside the first there are the boot files and a folder named "dtb",
I copied the "rk3528-vontar-dq08.dtb" file into the "rockchip" folder that is inside the "dtb" folder.
I then edited the "armbianEnv.txt" file, changing this line:
fdtfile=rockchip/rk3528-evb1-ddr4-v10.dtb
into this:
fdtfile=rockchip/rk3528-vontar-dq08.dtb