By default, Pulse SMS will send any conversations that you swipe away to the archive (which can be accessed from the app's side menu > Archived conversations). That archive is really what acts as the "trash can" for Pulse SMS. Conversations can be restored from there and are automatically restored when you get a new message.
If you did turn on swipe to delete in Settings > Swipe Actions and deleted the conversation, then unfortunately that conversation is really gone. There is no way to restore a deleted conversation.