Suggest you speak to Minivator, Watery,loo. I guess brake would operate when power is removed , so could be mechanically jammed , but don't mess unless you know what you're doing , visions of stairlift rocketing down non stop .
Sorry but as said you should ask the maker or on a dedicated forum (If you can find one)
The reason is: The stair lift is electric, but that does not mean an electrician will know how to fix it. Electricians will run in a supply, connect to provided equipment, but to fault find (Which is what you are asking) they need the relevant information, hence the replies you have had.