Configure AWS to allow my client to access their RDS/MariaDB database from MySQL Workbench

I have an AWS architecture set up am hosting a live service for my client. I have and RDS/MariaDB database to which the client needs to have access to maintain data in tables for which he will use MySQLWorkBench. I need assistance is configuring the remote access to be secure both for his own data management and also to prevent access to other client services within my infrastructure but need someone to set up the most appropriate configuration and security.