AW15R3 does not recognize its own Toshiba NVMe

I attempted to clean install Windows 10 on the Toshiba NVMe came with my 15R3 system. The only way I can do it is through Legacy mode, load Intel RST drivers and install Windows 10. However, after setting up Windows 10, I installed Intel Rapid Storage Technology software, but the software no longers detect my Toshiba NVMe anymore. When I switched to UEFI boot mode, the BIOS does not show hard drive as boot option (Legacy mode does). Any idea what is the cause? I think during setting up in Legacy mode, all of my disk automatically formatted as MBR. Is this the reason why the UEFI and Intel RST software cannot recognize the disk? I have updated the Toshiba Firmware from Dell  Support site.