I doubt you have a hydraulic drive, I believe they only shipped a handful before they bought National-Wheel-o-Vator and made the Destiny there default Residential Hydro offering.

What you're describing makes perfect sense, the chain is twisted and the elevator is in the pit, the lift has gone on slack-chain safety.

There is a bracket on the counterweight rails for this, when the chain goes slack it locks onto the rails to prevent it from free-falling. You will have to run the unit up on a service pendant to get it to release then manually reset the slack rope switch.

I would not do this lightly without experience and the proper tools. In reality you need to find out why it went on slack and access. It could have been anything from over-weighting the car to having a mechanical failure causing binding in the counterweights. Let me know where you are located and I may be able to recommend a company.