Thanks for the information, but unfortunately, they did not give information about how to open the the closed couplers that are not connecting two cars.

I just bought the train set (with which, I have no experience or knowledge) and in trying to connect  the cars, some of the couplers closed. I have no idea (and there is nothing in the accompanying information)about how to open the couplers; so I can couple the cars.

I would appreciate information about how to open the couplers.