By default, Pulse SMS will send any conversations that you swipe away to the archive. That archive is really what acts as the "trash can" for Pulse SMS. It can be accessed by going to the app's side menu > Archived conversations. Conversations can be restored from there and are automatically restored when you get a new message.
If you actually deleted a conversation or message, then it is really gone. There is no way to restore a deleted conversation/message.