First you should check in Dell, if the NVMe drive is supported by this computer. As far I know, only SATA II (even not SATA III) is supported. So, probably the NVMe drive will not be even recognized, forget about booting. You didn't mentioned what is the O.S. you have installed on this PC?
Leon is correct. First of all, if the BIOS does not have enabled UEFI support, you cannot use NVMe drives. Secondly, unless this PCIe NVMe adapter provides a UEFI OpROM to support booting, you will not be able to boot from the NVMe drive nor will you be able to use it as your system drive.