Mirakl marketplaces require that one of your product images is the default image, shown on the product page by default. For fashion retailers, this is usually a 'flat lay', or an image which shows the product lying on a white background.
You have a few options for selecting which of your product images is the flat lay, depending on how your source images are ordered.
The easiest way, if your images are all in the same order in shop, is to select which item is your flat lay image via the settings of your Harvey Nichols channel in Shipatron.
Settings > Harvey Nichols > Settings > Cutout / Flat Lay image position
More documentation here.
If your images are not all in the same order in Shopify, you can alter these on a case by case basis in Shipatron using out Image Translations feature.
Products > Click to open product popup > Translations
Select:
You can then reorder the images to the correct order. Bear in mind that the selection of Option 1 will still play a part in which image is selected as the flat lay.
More detailed information on how to upload alternate image sets can be found here.