I have a Dropdown from which you can select an existing entry from my database.
Beneath it are read-only textboxes which display all the other associated fields of that particular row that was selected from the dropdown.
When the page opens, everything is reflected correctly as per the default dropdown selection, however, when I change the item in the Dropdown, I'd like all the read-only textboxes to also change to reflect to correct values associated with the rown of my dropdown selection.
Try using a onChange function.
https://www.wix.com/corvid/reference/$w.ValueMixin.html#onChange
So something like this
export function dropdown1_change(event, $w) { //Add the rest of your code....
https://www.wix.com/corvid/reference/$w.Dropdown.html