As Montana says, you can easily hurt, maim or kill yourself. If you aren't completely comfortable around things like this, and have a healthy respect for what can happen, it is probably best to call someone who is. Also, when things aren't working right, they can be more unpredictable.
That said, you are right, that lift nut must be fixed to the platform or the acme threaded rod will just spin and not move the platform.
Do you have any manuals, schematics, etc?
A zoomed out photo of the lifting mechanism may help.
See if any of these parts look like they are similar...this company sells elevator/lift parts and here is a search for national wheel-o-vator lift nut ("nwov nut"):
https://access2parts.com/search.php?search_query=nwov%20nut§ion=product