A torsion spring under tension can put someone in the hospital, and that risk doesn't go down because the door is older - if anything it goes up, since a 1979 spring has more corrosion and more fatigue than a new one, which means it can let go in a way that's less predictable than a fresh spring would. We won't talk anyone through replacing one over the phone.
What you can safely check yourself: whether the door is actually off its track versus just misaligned, whether the opener's safety sensors are blocked or dirty, and whether a cable has simply slipped off a pulley without snapping. If the door won't move and you can see a gap in the spring coil above the door, or a cable hanging loose, stop there and call. Trying to force a door back onto bent track on a house this age usually bends the track further and turns a repair into a track replacement. The one thing worth doing yourself: unplug the opener before you touch anything, so it doesn't try to drive a door that's already off its rail.