Update DB table with dropdown selection field's value selected by user

Hello I’ve two questions about chronoform7 settings.
I have a dropdown field (field_1) connected to a table {table_1}in my database

The table_1 has these fields
event_id, event_name, seats

The dropdown value is table1.event_name
The dropdown text is table1.event_name

After the selection of the event I have to show in a text field or in a custom html code (field_2) the number of seats corresponding to the value selected (table1.seats)

How can i fill the (field_2) with this value?

Then the user have to select the number of seats to book (field_3)

When I submit my form I have to update my table1 subtracting the number of seats booked to the total seats
How can i write in a custom code php, the update query with the value selected of the form?

Anyone who can help me also for payed service?

to load a dynamic value you will need the load AJAX feature, you can use that to load data into the HTML view, I can try to prepare a demo form or video for you, please send me a message using the contact page!

Thanks for reply, I've sent you a private message.