There is a rod tht the trunk handle pulls on to unlock or release the trunk latch. It may have become disonnected and needs to be re-connected. If you can get to the latch from the inside there should be an, "Escap or Emergency Latch Pull", that is required in vehicles since 2002. I am not sure if it is required in trucks, but most NHSTA saftey requirements are for all vehicles. If you do not have one you may be able to unlatch it by grabbing the rod, some trim pannels may have to be removed which are held in place by number two phillips screws and body plugs which pull staright out just be gentle with them, and pulling on it where it should be pulled on by attachment to the handle. It may be difficult to get to as some trim pieces may be held in by the fact that the hatch is closed. You might have to carefrully work them out or work under them with them partially attached. The latch is at the bottom, so hopefully there is an escape or inner releasa that will make it easier.
The latch can also be released if you can get to the latch key which is a flat plate right next to the latch plate which grabs the U-Bolt that holds the hatch in place. This is the part that the emergency release and the handle release rod are attached to. So, if you can move it with a flat bladed screw driver the latch will come open.
The important thing is mot to use excessive force while doing any of this as everything does not take much force to actuate or when removing trim parts they do not take much to pull off. If you have to force it then something is being done incorrectly.
If you cannot get to it yourself by these methods, you will have to take it to a body shop to get it opened and the handle attachment fixed.