If the changes you made have not been saved back to Projectplace and you have the Projectplace add-on installed, please go to this location on your computer:
C:\Users\<your Windows user name>\Projectplace\Downloads
You can also right click on the Projectplace app icon on your taskbar (Launch bar on a Mac), select Preferences and then Open folder.
If you have not found the document there, please look for it on your computer in the application it pertains to e.g. for Microsoft Word, see recent documents section.
If the file is not saved on Projectplace or found on your local computer, it is unlikely that it can be restored.