Hi again, I’m just coming back to this once more!
I realised I’m not 100% which field I should be updating.
I have a Radio Button (size) that is an option on image attachments.
I also have a Gallery field that holds those images.
I’d like the images to take the default value (med) when they are uploaded or a page with a gallery is published (as the gallery might contain images that don’t have a value set by the user yet)
Do I use the update_field() function on the gallery field or the radio button?
I hope that makes sense…