If the “Featured Image” box doesn’t appear below the “Store Map” in the page editor, then it’s either set to hidden in the Screen Options tab, or your theme doesn’t support Post Thumbnails.
The Screen Options tab is located in the upper right corner of your screen. If you click it, you will see a list of options that you can show or hide.
You should see “Featured Image” in the left top corner. Make sure to tick the checkbox to make it visible.
If the “Featured Image” option is missing, then your theme doesn’t support it.
Add Post Thumbnail Support to Your Theme
You can add support to your theme for Post Thumbnails by adding the following code to the functions.php.