Best design patterns to use in a system that validates information between two databases

I was wondering if someone could help me by pointing the topics I should study to build a system described below. I am new to GoF design patters and I want to make sure I have a good modularization in this system because I am looking for scalability and constant implementation of new features.

I am trying to create the sketch of a system that will do, among other things, the validation of information between database A and database B. Please note that I have write and read permission to database A and only read permission to database B. So, a thread will periodically query data from database A and, depending on what it receives, it will query more information from database B, validate the information, and update database A.

New features for this system would be new types of validations, where different information will be queried and compared.

Can you please give me some insights of the design patterns that are mostly used to do tasks like these?

Thanks a lot, Mauricio