dired-unmark-backward
dired-unmark-backward is an interactive compiled Lisp function in `dired.el
'.
(dired-unmark-backward ARG)
In Dired, move up lines and remove marks or deletion flags there.
Optional prefix ARG says how many lines to unmark/unflag; default
is one line.
If the region is active in Transient Mark mode, unmark all files
in the active region.