MVD is not support working with exists database but actually you can do it.
First, there is two rules for exists database to be compatible with MVD.
1. Every database table must have primary key "id"
2. Foreign keys must have names like "id_tablename"
if your database meets these requirements, you can start to create your project using SQLite database, to create tables and fields like in your exists MySQL database. You do not have to create all tables and fields, just only those that will be used in your project.
After that you can just switch your project to MySQL DBMS and connect to exists database.