we try install firmware for avalon 920p on raspberry pi 3 model B+ but not work good . must on model B only .
i hope found firmware support model B+
If you already check the download.canaan-creative.com and no for model b+ it means they don't support this raspberry model I suggest look to someone who has raspberry pi 3 model b and make a deal to swap yours to his Raspi or buy rpi 2 model b which is a bit cheaper rasp3 model b.