You can change it to legacy mode yourself. F2 on startup.

I wiped the drive and converted it to mbr, but the option is greyed out to switch to legacy. I have both Windows 10 and Windows 7 on usbs in mbr boot mode, and my drive is as well, but my motherboard isn't letting me change boot mode

options grayed out

The win 7 OS disk may be MBR and require legacy mode enabled in BIOS. 

If may also help to pull out the win 10 GPT disk. 

it is mbr ive tried everything even switched my hdd into my brothers pc and it worked its just my mobo on my pc wouldn’t let it work cause it needs legacy bad mobo:(

Did you install/set up a second Windows 7 boot drive presuming factory installed OS is Windows 10?
It is easier to uninstall factory hdd/ssd and install your own hdd/ssd then do a fresh clean install of Windows 7 via uefi bios on it.

R9 bios System setup options—Boot menu

it seems this should be available to user unless there is a system or administrator password set up.  can you confirm there is no password set up?

try clear CMOs settings if still no change.

theres no password setup

even after doing so its grayed

@aruuu Legacy will be greyed out until you disable secure boot. Then you can switch from UEFI to Legacy.