How to change prices in Open Cart in certain categories?

Question

PHP

Faced such a task, there is a store on opencart 1.5.6, it has several categories, let's call them (A, B, C and D)
Products in categories A and B are created automatically through the parser and prices there are allowed in hryvnias, and in categories C and D, products are added manually with prices in dollars. The problem is to make some field in the admin panel in which you can set the dollar rate and after that, so that the prices of goods that are in categories C and D are multiplied by this rate, and the prices of goods from categories A and B remain unchanged. Tell me what files need to be edited to do this? more precisely, how to find out what category a product has, because as far as I know, opencart has problems with this and a product can have several categories at once or something like that. There is practically no experience with open cart, and there is not enough time for the scientific poke method ...