Repairing UEFI boot manager

I just had my computer updated with a new motherboard. Replaced an MSI B-450 with an Asus ROG Crosshair VII Hero x470. Now I cannot boot into Linux. I'd had trouble before and from the BIOS I'd select the drive Linux is on. But with the new board all I get is an error telling me the drive is not bootable. A tech at the place that replaced the motherboard said that there should be a way to add an new boot option on the motherboard. But can't seem to find where on this board. We located the boot device and have a path to it, but where to enter such information. I can reinstall Linux, but would rather fix the boot manager to show both OSes. I do have a live version I can work from.