I spoke with Dell pro support and they couldn't find an answer for this. They just said to use the drive that came with it. 
I take the NVME drive from my Latitude 7490 laptop and put it in a new 7420 laptop. Both are Pentium based machines, both running Win10 at the same level. I've done this many times before on different computers. Take drive from one machine, put it in another like it, then go. This time I get a message, "inaccessible boot device". I've tried Acronis universal restore and Windows PE bootable, but it doesn't fix it. But then I put the NVME drive into a Dell precision desktop and it boots there! I think it may be because of some Microsoft change. Anyone have an idea how to get around this? Thanks, Al
Can't boot drive on Latitude 7490 when I put it into new Latitude 7420.