HI Sangram,
1. Create a date rule to capture the third day after assigning the complaint. and assign that to a date type.
ex: Warning date = date of complaint assignment + 4 days.
2. Add this date to the date profile that you have assigned to action profile and sales order.
3. Then in action write a condition warning date = today.
Then the action will execute on the fourth day after assigning the complaint.
Regards
Ravi