If you have a QTS 4.3 and previous Xopero installation on your QNAP, remove it before proceeding with the following steps - you will keep your data.
Container station installation
After logged in to the QNAP panel, go to the App Center. Then on the left side select the All Apps tab, find the Container Station and install.
After completing the steps above, you only need to install Xopero BETA 3 x86_64 version.
To install the package, go to My Apps and select Install Manually option.
Then in a window, you have to select the location of the package and click Install.
After performing the above steps, the installation will start. During the installation, in QNAP logs will display the information and warnings about the installation process. The screenshot below shows the correct database migration process.