# change directory to target folder:
cd /Volumes/path/to/folder
# find all things of type "f" (file),
# then pipe "|" each result as an argument (xargs -0)
# to the "xattr -c" command:
find . -type f -print0 | xargs -0 xattr -c
# Sometimes you may have to use a star * instead of the dot.
# The dot just means "here" (whereever your cd'd to
find * -type f -print0 | xargs -0 xattr -c