In Old phone

1. Open application and export database from Settings >> Chat Settings >> Backup & Restore Messages >> Manual Backup >> Export To External.
2. Exported database will be stored where the user chooses to export it.
3. Now get that database out of your phone (Maybe via email or using USB storage).

OR

Open application and export database from Settings >> Chat Settings >> Backup & Restore Messages >> Backup on Google Drive >> Select account >> Backup.

In New phone

1. Install “Calculator Pro+” application.
2. Now copy the database from where you have stored it from the old device.
3. Open application and Import database from Settings >> Chat Settings >> Backup & Restore Messages >> Restore Backup >> Import from External. It should show the database to import.
4. Select the database to restore messages.

OR

1. Open application and import database from Settings >> Chat Settings >> Backup & Restore Messages >> Backup on Google Drive >> Select account >> Restore