Code for replacing and deleting data from MySQL db

Hello everybody.
I have a problem. In my database I need to delete special rows of duplicated contractors from “contractors” table. Last (which always have the same individual vat_number) added duplicated contractor must only stay. Any other rows with duplicated contractor_id are to delete.
Second thing is that this old contractors (contractor_id) are in invoices in the second table “orders”. I need a script to connect to mysql database and find all invoices having old contractor id and replace it all to last created contractor_id with the same vat_number.
Can somebody help me in this?

Here’s the example:

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