You can move data from the CPT UI to the Meta Box with the help of the MB Custom Post Types & Taxonomies extensions. It will save a lot of time and shorten the process dramatically.
1. Backing up the data
Remember to back up your data before migrating to avoid unexpected events.
Here is my example. I have this Companies post type created by CPT UI with all the posts inside.
As you can see in the Plugin menu, the CPT UI has already been activated.
I will now proceed to transfer the data.
2. Installing plugins
I'll install and activate MB Custom Post Types & Custom Taxonomies.
After that, the new Post Types menu appears on the Dashboard along with the CPT UI Migration sub-menu.
3. Migrating the data
Go to the Post Types menu > CPT UI Migration > Click the Migrate button.
When the process finishes, it will show a "Done" message.
Note: The CPT UI menu will automatically disappear when the migration process finishes. This is because Meta Box automatically deactivated it to avoid conflict and errors caused by registering the same post type.
The Companies post type and all the terms in the Company Types taxonomy are still there. They are the new ones created by Meta Box. It also means that all the data was migrated successfully.
And the CPT UI has already been deactivated.
The migration has been done.