Hello,

You did not mention the header before. You told about the shop page background.

Please add this code to the Theme Settings > Custom CSS > Global:

.main-header, .sticky-header.header-clone, .header-spacing {
    background-repeat: repeat;
    background-attachment: scroll;
    background-image: url(https://phoenixcareuk.co.uk/wp-content/uploads/2019/11/k-background2.jpg);
}

Change the image URL as per your needs.

If you want to change it only on the shop pate, add this code to the page settings of the shop page.

Best Regards