If you wish, you can use the same policy if your travel start date is within 15 days of the policy start date. Or you can get the dates changed before your policy starts. It can be changed after policy start date too but then you have to give proof that the travel has not been undertaken i.e. your passport copy, tickets etc.
If the duration of your trip has reduced, you can save money also by getting dates changed. In any case, if your travel start date is postponed by more than 15 days, the current policy will be void, so better to get dates changed.
For this you can put in a service request at the link given below: