We can initiate firewall immediate reboot or schedule a firewall reboot at specific time period from NSM.
Steps to Reboot/Restart a firewall or group of firewalls from NSM:
1) Login to NSM, Firewall-->Inventory-->Select the required group of the firewalls which needs to be restarted. Click on the Actions icon (3 vertical dots) next to the specific group.

2) We can select specific firewalls from the list for reboot. Also, we can choose to reboot Now or Later based on the schedule.

3) Firewall/Firewalls will be rebooted in 3 seconds (approx.)

CAUTION: This option should be used with caution during the scheduled maintenance window.