You can manually back up your chats to Google Drive at any time:
Go to Menu button
Tap Back up to Google Drive and select a backup frequency other than Never.
Tap Back Up to begin your Google Drive backup. This process may take a few minutes.
Note: Depending on the size of the chat, the first complete backup could take a while. We recommend that you connect your phone to a power source. However, subsequent backups are incremental, thus not requiring a completely new backup of all your data every time.