How can I update the product quantity with the uploaded file count?

If you want to update the main product quantity to match the number of uploaded files, follow the steps below:

Enable setting

In the app, on your Upload field config page, in the File settings section: 

Allowed number of files > Multiple files  > check "Update quantity to match count"

Enable quantity selector in theme

The app will look for the quantity selector on your theme to update with the current upload file count.

Make sure that you have the quantity selector enabled on your theme.  Depending on your theme the setting can be on different locations in the theme editor.

On the Dawn theme you can add a block "Quantity selector" on the product template:

Updating required file count from selected quantity

The setting above always runs from files to quantity: the number of files the customer uploads sets the product quantity in the cart.

The reverse is not directly supported. There is no setting that reads the quantity the customer selected and then requires that many files, so a shopper who picks quantity 3 is not forced to upload 3 photos.

Using custom JavaScript it is possible to dynamically change the required file count based on the selected quantity, however this requires adding a script that listens to your theme specific quantity selector and updates the field's fileCountMin  setting accordingly. Visit the JavaScript Upload field update config to learn more about how to update the field's configuration dynamically.