If you have access to the driver's seat of the car, then check to see if there is a trunk release button located somewhere inside the car. It is often located under the steering wheel or on the main console of the dashboard. If you know that the car has a trunk release button inside but you cannot get inside the car, then it will be easier to prise open the driver's side door and then use the button to open the trunk rather than trying to prise open the trunk first.
As long as you can get into the car, then there should be other ways to get the trunk open from the inside. If the back seats of the car fold down, then you should be able to crawl into the trunk space where there should be a trunk release latch that will release the trunk door from the inside.
If none of these options are possible, then the best course of action is probably to either call a locksmith or a car breakdown service, as professionals are likely to be able to prise the trunk open causing as little damage as possible to the car.