You need to go to AMD Support and turn in a Warranty Request Form for a AMD BOOT KIT. This is the answer I gave to another User if a similar problem:
Ellis Rodriguez (to miller)1 day agoRe: I have a 2700x that i cant boot on my Gigabyte ax370 gaming 5. WHAT TO DO????
Need to get the latest BIOS from the Motherboard's Support Site that supports the new CPU.
Then you are going to need to request a AMD BOOT KIT to flash the new BIOS on your Motherboard. Unable to Boot New Desktop System Configured with AMD 2nd Generation Ryzen™ Desktop Processor, and A... .
In the above link it has a link to AMD RMA form for you to start the process to get a Boot kit: AMD Warranty Request Form
The AMD BOOT KIT provides a Ryzen that the motherboard supports thus you then are able to flash the new BIOS to the version that supports the new Ryzen CPU.