I'm having difficulty changing the page orientation of one page from landscape to portrait, while keeping other pages as landscape.
Is there anyway that this could be done?
I don't know what version of Corel you're running, but I imagine earlier/later versions have a similar option. In CorelDRAW 2017, select Layout > Page Setup... :
Adjust the width/height as necessary, and check the "Apply size to current page only" box: