If the post or page was already shared on Facebook and it's not showing the right preview image, also known as Cover Image, or you want to switch things up, the changes might not be visible.
That's because Facebook relies on its cache; sometimes, it needs a good clearing to display the right image from your website.
For cases like this, Facebook provides a tool called Facebook sharing debugger.
How to use Facebook sharing debugger
Go to Facebook Sharing Debugger by clicking on this link
Grab the URL of your page or post and paste it into the Sharing Debugger field
Click on the Debug Button.
Look for the Time Scrapped option.
If the time/date is in the past, click on Scrap Again to clear the page from Facebook's Cache and the new meta information is correctly indexed by Facebook.