Hi there, @diamondcare.
I'd be pleased to help share information about converting QuickBooks Desktop (QBDT).
A company file can't be opened in another region's of QBDT version. Therefore, there isn't an option to convert directly from QBDT Enterprise 2016 to QBDT Enterprise 2019. If you wish to, you may have to cancel one service and subscribe to the global/international version.
On the other hand, you can import/export using the IFF file to ensure the platform/feature difference of the version wouldn't cause any issue. Make sure that you have installed QBDT UK with the UK license, then restore the file.
To learn more about company file compatibility, you may read this article: Company file compatibility with QuickBooks Desktop when upgrading.
You're always welcome to add a post/comment below if you have any other questions about converting QuickBooks Desktop. I'll be right here to help you however I can.
