This was Petra response:
thank you for your message.
If there is not enough free space to build new buildings at the station, you can move, store or sell already existing buildings in order to make more space for the new ones, please see: http://prntscr.com/b204n8
If you have any further requests or questions, please do not hesitate to ask.
Have a nice day and a lot of fun with Train Station.
But I have not built anything at that location yet. So that means that there are no buildings that can be moved or sold. The only thing at that location is building that came with the station. and decorations, I clicked on each one of them and none can be moved or sold. I don't understand what else I can do.