Create a GPO and navigate to:
[Computer Configuration\Preferences\Control Panel Settings\Scheduled Tasks],
Right-click in the right-panel, choose Scheduled Task (Windows Vista and later):
1. type a name and choose SYSTEM account to run this task.
2. Switch to Triggers tab, click New, choose Weekly (or any date you prefer), click OK.
3. Switch to Action tab, click New, type «defrag.exe» in Program/script box, type «/C » in Add arguments box. Click OK. You can choose other parameters based on your need. Type defrag /? Get more information about this command.