Detailed Lannouncer instructions are at this link You need the Lannouncer app on your Android (also works on Kindle Fire) device, and a LanNouncer DTH added to SmartThings.
Test your Android device with the Lannouncer DTH in Smartthings. It should talk and make some siren like sounds.
In Big Talker, set it for use with the Lannouncer Device, then create the text announcements
One big gotcha with using Lannouncer. In your router’s DHCP settings reserve (fixed IP address) the IP address for the Android device, or it will stop talking when the router resets its IP address table.