Have you tried CTRL+C and CTRL+V, or CTRL+INSERT and SHIFT+INSERT?
If both not working, you can export the aia of old project and new project. Unzip the old aia, move the relevant blk and scm file into the new aia. And you need change the screen name if necessary, both file name and content of the file.
blk and scm both are text based file, can be opened by notepad.