Navigate to edit Promotion Rule and select type Trial from 'Rule type' drow down.
With Trial promotion rule, configure duration of your FREE trial.
Select 'Condition' section to edit rule conditions.
Using the Free Trial field you can set the number of periods a subscription can be in trial mode. Enter the number of trial periods and select a period choice. Trial period can be any of Hour, Day, Week, Month, Year. Learn more about Trial Management.