You'll need to remove the M.2 SSD -- on systems with both an M.2 and a 2.5" drive, the M.2 must be the boot device.  
I have done clean install of Windows 11 on new  SSD  M.2 on my system and now it shows as C drive. My old windows 11 and data is on HDD which is Partition D.  I would like to boot the system from HDD (D partition)  to backup my data but I could not find any option to start the system from that partition.   I have tried with F2 as well as F12, however there is no option available to boot the system from HDD.  After the backup I would like to format D partition and start using C partition on the SSD. In the Boot section in BIOS UEFI is clicked as default. I would appreciate your help.  Thanks S K  
Boot Sequence - SSD and HDD - Dell Inspiron 17 - 7773