The latest version of macOS ("Catalina") added an extra layer of security that requires developers to have Apple virus check their software. I have not put Dashcam Viewer through this additional hoop yet which is why you are seeing the message. You can easily bypass this using the procedure below.
If you see this message, you can run Dashcam Viewer by going to your Security & Privacy settings and selecting the “Open Anyway”.
More details here:
“How to open an app that hasn’t been notarized or is from an unidentified developer”: