What is the exact system model?
Assuming you have Win 10 OS installed, kindly review these links to set the external display to primary.
Hope this helps.
Also, please click my DELL-username and write me a private message with the service tag and your Name for case records.
Let us know if you have any other queries.
Thanks for the reply. But, I want to make my external monitor as primary before booting into Operating System. Kindly let me know if there is a way to do that in the UEFI boot mode.