As shipped, the drive will be in IRST/RAID mode.  Pause the install with F6 when indicated and have the driver linked below on the flash drive.  Load it and the installer will find the drive.

Be sure you remove the original drive from the system before you load a new coy of Windows onto the new drive.

Intel RST driver:

Third link here:

https://www.intel.com/content/www/us/en/download/19512/intel-rapid-storage-technology-driver-installation-software-with-intel-optane-memory-10th-and-11th-gen-platforms.html

why remove the original drive, i would like to keep original drive as windows 11 and 250 gb drive as windows 10

Hi @Shkhaslam welcome to this free user-to-user Alienware laptop discussion forum. 

Are you sure that Alienware X17 R2 came with a small 1GB drive and not a 1TB drive. Check Storage Options on Alienware x17 R2 Technical Specification | NotebookCheck.net.  

Alienware x17 R1 review | NotebookCheck.net says supported NVMe storage devices are one PCIe4 and one PCIe3. The Alienware x17 R2 review | NotebookCheck.net does not clarify what NVMe storage slots are available.  

There is option How to create a dual-boot setup on Windows 11 | Windows Central, which can use the PCIe4 slot as the (C:) boot drive with option to use the Windows 11 or the Windows 10 x64 operating system. 

Thanks for the reply

my bad, it came with 1 TB pre installed with Windows 11, the above article does not help with how to install Windows 10 on the second SSD i installed.i tried installing win 10 on the other drive but it cant find the hard drive. Tried installing with nvme drivers too, it fails

Hi @Shkhaslam thank you for sharing update. 

The BIOS Main page lists the drives, if 250GB SSD not listed, it has not been electrically installed correctly. Please reseat to ensure 250GB SSD is installed into the electrical slot of the PCIe socket. Go to Disk Management to format 250GB SSD and assign partition letter so that it can be used. Create Windows 10 x64 Version 22H2 installation media. Download Windows 10 (microsoft.com).  

Having installed Windows 10 x64 on the 250GB SSD, change the F12 Boot Menu to list the boot drives so that option to boot from Windows 11 or Windows 10 x64 SSD is enabled.  

In BIOS i can see my 250 GB drive But during installation windows 10 cant find any drives to install.

Hi @Shkhaslam thank you for sharing update. 

Does 'This PC' include the icon and assigned letter for the new 250GB drive? 

Yes, it shows the drive

Hi @Shkhaslam thank you for sharing update. 

Excellent, now ready to install the Windows 10, 64bit operating system on the new 250GB drive. Remove the 1TB SSD drive so that Windows 10, 64bit can be installed on the new 250GB drive. Create Windows 10 x64 Version 22H2 installation media. Download Windows 10 (microsoft.com).