Here is the bcdedit script we use for UEFI (if that's what you mean):

bcdedit /set {bootmgr} device partition=s:

bcdedit /set {memdiag} device partition=s:

bcdedit /set {default} device partition=c:

bcdedit /set {default} osdevice partition=c:

bcdedit /set {FWbootmgr} displayorder {Bootmgr} /addfirst