How to transfer/connect a MariaDB db from OH2 to OH3?

Hello, I need help connecting the old db to my new OH3 installation. If I do it straight, then I get errors that some tables have different types (old=double, new=charset). Do I have translate the contents of that tables or is a distinct setup to be done or is there maybe a tool for translation?
Is there any reason that OH3 build a new table “items” and how the old “Items” and the new “items” relate to each other?