Freeze Spell for Howling Blast

[Pekisa7]

Hello everybody its Pekisa7. I need help. I want the howling blast spell which I based on blizzard to freeze at least 5 units in place so they don't move or attack for a short amount of time. Then they unfreeze and start attacking again. Can someone tell me how to do the triggers? Best regards from Pekisa7.