How to Upgrade/Replace the PCIe SSD in a 21.5-inch iMac (Late 2013) iMac14,1 iMac14,3 - YouTube
Amazon.com: PCIe NVMe Gen3x4 SSD 1TB 512GB 256GB 128GB 3D TLC NAND Flash Hard Drive SSD Replacement for Macbook Air 2013-2017, Macbook Pro Retina 2013-2015, iMac 2013-2017, Mac Pro 2013, Mac Mini 2014 (1TB) : Electronics