GPO can be restored by powershell with the following cmdlet
Restore-GPO -Name “Default Domain Policy” -path <path to GPO backups>
As well as powershell, GPMC can be used to restore. To restore using GPMC, right click on the GPO and select Restore Group Policy Object Wizard, specifying the location of the backed up GPO.
Select the version of GPO you want and click next and finished.
To restore a GPO that has been deleted, on the Group Policy object container, right click and select Manage Backups. Browse to the location of backs, select the required GPO and click Restore.