Featured image custom size

Hi,

I am using a child theme of Squarex Lite which I developed myself. I have changed the settings of the header to take all the screen minus the navigation menu on top.

However, the header image size is too small for the size of the screens I am going to display this on –?I would like the featured image to be 1920px wide.

I tried copying the thumbnail function from the parent theme’s functions.php to the functions.php in my child theme but it doesn’t seem to be working as the header image is still only 1400px wide.

Could you please help me change that?

Thanks!

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