Reloading projects

Mac OS 10.13.3 I am trying to reload a project and the data file is there but not the app file. Is there any way to retrieve it please.

Audacity needs the MyProject.aup file and the MyProject_data folder (for example). The folder is useless without the AUP file. What happened to the AUP file?
– Bill

No idea, just seems to have vanished. It is not in the trash and I usually keep my files pretty well. I can only thinks I may have accidentally deleted it. If it had been an intentional delete, I would have done the data file too. Oh well, thanks for your help. Back to the drawing board.