IBM 5150 Manual To Operations page 90

To Correct a Typing Mistake
There are several ways to correct a
mistake that you notice before you
press the Enter key.
[I.EJ]J
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One of the easiest is use the Backspace
key to move the cursor backward, under
the leftmost wrong character. The
Backspace key deletes characters as it
moves the cursor to the left. (The
Backspace key is located on the top
row next to the Num Lock key.)
Now type the correct characters, and
press the Enter key when everything
is the way you want it.
Another way, if the line is just too
messed up to worry about, is to press
the Esc (Escape) key. A Backslash (\)
is displayed, and the cursor moves ,,-......,
down one line on the screen. This
cancels the messed-up line and you
can then type the command correctly.
More ways to correct typing mistakes ("editing") are
discussed in the Disk Operating System book; but these
two keys should be enough to get you started.
DOS 3-16