Can you use Subtables with Existing database?

I have an existing database with table names such as
Customer and Invoice. PHP/MySQL

I have already developed the system based on this database (amongst other tables).

For me to use nested repeats would I have to rename my tables and manage it through Database manager? I mainly use Navicat to manager my db.

I won’t be able to rename my tables. Too much has already been developed.

Also, which would be the more suitable tutor for Nested Repeats?

Or