What was the error message? Can you show us?
The easiest probably is copy/paste the *.lfm and *.pas files to new project's folder. And then use the Project Manager > Add > File from the File System.
Actually you don't have to copy/paste those files to the new project's folder, but if you move the original source code to other location or rename that folder, you'll get error. Unless you properly manage your project folders and have a shared library folder.