On an actual typewriter, backspace just moves the head one character backwards. It doesn't inherently erase anything

But if you do want to actually erase text, there still is a way - many typewriters had multiple ink ribbons. In addition to black, you might have red for indicating deficits in accounting, or for erasing text you'd have a white ribbon.

So "erasing" on a typewriter is basically just typing the same text over the top again, this time in white so it doesn't show against the paper.