By default using ./bin/add-user.sh|cmd file should work.
But if add-user.bat result a failed resp by The system cannot find the path specified. message, you may go like following
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head into the wildfly root folder.
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use following command (template)
java -Djboss.server.config.user.dir=<<address of configuration folder, example: ./standalone/configuration>>
-Djboss.domain.config.user.dir=<>