1) put your key in the keyhole and try to rotate it right or left (I forget which one it is) to confirm if the "valet" function was engaged and that's why your interior lever isn't working. Don't force the key if the cylinder is seized (don't break the key!), they sometimes can seize by corrosion if not used for a long, long time.
2) if you still cannot open it, either from inside by the lever or outside by the key, then fold down the rear seat and take a flashlight and a trim removal tool (I can't remember if it is a philips to unscrew the centers of the luggage door trim clips, or if it is a forked trim push pin removal tool) and pull the trim back enough to get access to the luggage latch
3) at that point you should be able to move the lever to release the door
4) bonus round: if, for some reason, the latch has an internal failure making all levers inoperable, then you want to remove the mounting bolts from either the latch or the striker, whichever is more accessible to you, to get the door open, and then replace the components with junkyard parts
Additional thought: if after the above you have found the key cylinder is seized, they can sometimes be revived by remove and disassemble (keep track of which tumbler went in which slot), and either clean up and lubricate and reassemble, or remove the bad tumblers (usually it is just the one or two nearest the outside) and put it back together again. Your key will still work, but it won't be quite as secure as before (some other keys would then also work, with fewer tumblers), but the risk of that being an issue is super crazy low.
To disassemble the key cylinder, usually there is an "E" ring on the end to remove, then slide the center rotating portion out, and the tumblers will then be able to be pushed out of the housing. Just don't get them mixed up, or your key won't work any more.
Nuclear option: buy a used key cylinder from a junk yard and make sure it comes with its key, and then keep that somewhere secure for when you need to key into your trunk.