Press Insert to toggle between overwrite mode and insert mode. The current mode is displayed on the Status Bar. The text cursor must be enabled in the cell or in the input line.
On the Status Bar, click on the area indicating the current mode in order to switch to the other mode:
Insert mode is active. The area in the status bar is blank, when Insert mode is active. The text cursor is a blinking vertical line. Click on the area to activate the overwrite mode.
The overwrite mode is active. The text cursor is a blinking block. Click on the area to activate insert mode.