Product image thumbnails not being added through iOS app

Site URL: https://www.sasfabricscalifornia.com/search?q=cotton

Hello, I have been having a longstanding issue with SquareSpace product thumbnails. From SquareSpace's support website, https://support.squarespace.com/hc/en-us/articles/205812718-Adding-thumbnail-images, it says that thumbnail images automatically defaults to the primary image of the product. However, thumbnail images currently cannot be edited or changed from the newest SquareSpace iOS app. It also seems that since the transition to the new editor for 2021, all of the thumbnail images for products created prior to the transition are now missing, leaving our search page devoid of thumbnails and overall not useful for quick product previews. Is there a way to automatically make all products have their primary image be the thumbnail image after the products have been uploaded? Or will my team have to painstakingly re-upload thumbnail images for our thousands of individual products that are constantly turning over?