You need the database password.
Depending on how the fresh install was done, you may need to reset it to match the old password, or make a few changes after the restore.
The database password can be fount in /etc/fusionpbx/config.php on a working setup. If installed without customizations from install script, the database password will be random for each installation.
Code:
grep db_password /etc/fusionpbx/config.php | cut -d "'" -f2
will help you find the expected database password.