Hmmm... The App Builder is located in the project folder:
project\prodisttool.llb\build application.vi
Make sure this LLB is in your project folder. Also... have you changed the location of your "Library folder" under tools>options ? LabVIEW looks for the project folder inside your "Library folder" whose default is usually something like this on a PC:
C:\Program Files\National Instruments\LabVIEW\
So the App Builder should be at:
C:\Program Files\National Instruments\LabVIEW\project\prodisttool.llb\build application.vi
If you changed your Library Folder, LabVIEW might not be able to find it, and then you won't see it under Tools
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