not only.. but also

Why is this sentence incorrect: "Not only this transformation changes the preference of respondents, but it also converts the scale"

and I was asked to write: "Not only does this transformation change the preference of respondents, but it also converts the scale"

Any suggestion will be helpful.

This is called do-support and is required when you have a negative such as never before the subject.

Other examples from Wikipedia:

Never did he run that fast again. (wrong: *Never he did run that fast again. *Never ran he that fast again.) Only here do I feel at home. (wrong: *Only here feel I at home.)