First, you need to be logged to the Administration Interface of your QNAP NAS. Then, click on the App Center icon.
Click on the parameter icon in the upper right corner (cogwheel).
On the main tab, check the ‘Allow installation of non-QNAP Store apps’ box. Then select the second tab named ‘Application repository’.
In front of the Name field you will indicate “MyQNAP Repo”, for the URL field you will copy and paste
https://www.myqnap.org/repo.xml
and to finish, you click on the Add button.