You'll need to get under the car - safety first, of course.
Be sure to start with the emergency brake off. Once underneath, look at the area directly behind the differential, where you should see a sheathed cable assembly, part of which passes thru a coil spring and a fixed bracket. Notice that the sheath is retained by a 1" u-clip. The idea is to slide the clip to release/uncapture the cable allowing the spring to take up slack and adjust for wear, etc. No need to remove the clip entirely. If the clip hasn't moved in some time, you may need to gently pry/work it loose....WD-40 might help.
Once/if things re-tension, push the clip back in place so that it once again captures the park brake cable. Done.
This simple process of course assumes working components, so if completing it fails to restore normal operation you should inspect the related hardware including the springs on the rear calipers and the sheathed cables themselves, all the way up to the emergency brake handle and it's pivot. Of course good calipers, pads and discs help as well.
