IBM 5155 Manual To Operations page 207

[[[hJ]J
Pressing the Insert key enables you to add characters in
the middle of a line. Press the key again and you are
back to normal operation.
[1[dJJ
Press the Delete key and the character at the current
cursor position is erased; all characters to the right of
the deleted character move one position to the left.
+
\.
The Plus and Minus keys have no program-defined
functions. When pressed, they simply enter a plus or
minus sign on the screen.
Keyboard 3-19