How to personalize an item in the cart with a dropdown or box?

how to add a personalization to an item (like a jersey) in the cart with a drop down or box and have it change the image

At it’s most basic through theme customizations for textual information or file uploads

https://community.shopify.com/c/shopify-design/product-pages-get-customization-information-for-products/td-p/616503

To start having image editing, or overlays on product images, that’s advanced personalization either through advanced customizations, or apps.

If you need a personalization customization to get text,etc from a customer per product then contact me by mail for services.
ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.
Contact info in signature.