Which Gigabyte board do you have? If it's a higher end one like the Aorus Gaming 7, then just do a BIOS update throw in the 9900k and you should be good to go. If it's a lower end board like the Z370 Ultra Gaming, then you may hit VRM throttling with the 9900k under very heavy workloads unless you power throttle it. The 9900k is the most power hungry mainstream chip to hit the market since the FX 9590, and it needs some beefy power delivery to reach its full potential.