You don't have a button on your board. You will have to use the EZ Flash tool in the UEFI. Go here: https://www.asus.com/us/Motherboards/B150M-A-D3/HelpDesk_Download/ and download the BIOS you need to a USB drive. Access EZ Flash and choose to update the BIOS from a USB drive and install whatever version you need. Are you trying to run a Kaby Lake on that board?