There's a very small chance that the motherboard BIOS would have been updated already for you, in which case it would have a "AMD Ryzen Desktop 3000 Ready" sticker on the box, similar to this:
Quite unlikely though, so don't count on that happening.
Not sure where you're planning on buying from, but the vendor may offer the service to update the BIOS for you.
Since you're looking at a Gigabyte motherboard, Gigabyte can do the BIOS update for you in UK, but I assume you'd need to pay for postage costs. They also have a very helpful rep on these forums (username: GIGA-Man).
@GIGA-Man did I get that right on the BIOS update service?
AMD offer a boot kit service, where they'll loan you a cheap APU to enable you do the BIOS update.
Other option is to phone a friend.