If I understand correctly, you have already created a new device and applied the LANnouncer Alerter DTH to your Android tablet running at least OS 5.1? If so, then you should be able to select it in your SmartThings app and see something like this. I gave my Android tablet the name of “Living Room Speaker”. This device handler sets up your Android tablet as a siren, speaker, tone chime, strobe a light, and event take photos using the tablet camera. It should be more than just a siren.
I see in your screen shots that you have BigTalker currently configured to access a music player. You will need to re-install Bigtalker and configure it to access a Speech Synthesis device which would include LANnouncer.
Once configured properly, you can then setup BigTalker to send the output (%weathertoday%) to your LANnouncer device.