You need to start Lenovo Photo Master, then go to configuration settings and confirm the software as the default application for DVD launch. This applies only to the recognized media, and by recognized media I mean supported file formats that Lenovo Photo Master can open.
If you need additional information, I recommend you check the Help section of the software. Go to Help > Contents then use Search and type association. This will give you instructions on how to make the software the default application when you insert compatible DVDs.