Change the main product image in gallery

Hello,

please, how would I be able to replace path the full product image (which will be displayed when I click on the product image in the popup window ) e.g. for large size?

Because I use the Watermark plugin https://sk.www.ads-software.com/plugins/image-watermark/ and I need it to give me a watermark only for Large, Thumb, etc. but not Full (oroginal image).

But when I do not enable the Full Size option, the watermark does not appear on the popup image in the product but only on its thumbnaiil.

Look at this : https://prnt.sc/nvscof

I try add this code in function.php but it doesn’t work.

add_filter( 'woocommerce_gallery_full_size', 'dt_wc_custom_gallery_full_size' );

function dt_wc_custom_gallery_full_size () {

return 'large';
}

I need woocommerce to use large image (not large size) instead of full image.

Thank you advanced for help