How do you make the number one disappear by adding to it?

“Subtract one from it”

Subtracting one would not make the number one disappear; it would simply change the value to zero.

“Add a zero to it”

Adding a zero to one results in ten, not in making it disappear.

“Add the letter 'S'”

Adding 'S' to the word 'one' does not create a word that signifies disappearance; it just forms 'sone,' which has no meaning.