Question: How to set up the second monitor as extend screen on Windows 10?
Answer: Using keyboard, press and hold

and then press
P. On the bottom right corner, select
Extend option.
Question: How to select the primary monitor on Windows 10?
Answer: Right click on any empty space on the desktop and select Display Setting. Select the desired monitor enable Make this my main display under Multiple displays.
Question: How to change the sequence of monitors on Windows 10?
Answer: In Display Setting, drag the display icon to rearrange them.