Dear Friend,
There are five paths which save addin files, we usually use two of them:
C:\ProgramData\Autodesk\Revit\Addins\201X\ C:\Users\[user]\AppData\Roaming\Autodesk\Revit\Addins\201X\
maybe your computer hid file extenstion of .addin
or U could post your folder screenshot in this issue :)
Best Regards
Frank Liang
TJAD BIM Software Dev Lead