Do you know the model number of your keyboard?  You may be able to reset that without a key mapper.

That being said, the question you're asking has been asked and answered, multiple times, in this group.  One example: Accessible app to map menu key

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Brian - Windows 10, 64-Bit, Version 21H2, Build 19044  

Friendship. . . Intimacy, untroubled by eros.

         ~ Kim Chernin