Field select generate sql query and fill input field

Question

Hello. Good afternoon.

I have a form where there is a select field that brings dynamic values from a mysql database to select users.

I would like when an item is selected in this field, through an onchange or something similar, the value is sent to another sql query on the same page (in this case it is a modal, to help rs), where it would bring a database value from another table and automatically populate an input field that follows below the initial select field.

Does anyone have any idea?

Currently use classic ASP for this application.

Thank you.