On the last screen of the IRS Withholding Estimator, scroll down a little and click "How to Adjust Your Withholding." It will tell you how to fill out the W-4.
I don't know of any similar tools for state withholding, but you should be able to work it out from the instructions and charts for the state withholding forms.
For New York: Form IT-2104 (includes instructions)
For Connecticut: Form CT-W4 and the publication "Is My Connecticut Withholding Correct?"
Another approach would be to do pro forma 2020 tax returns with your 2021 information as an estimate for 2021. It would be easy to do that if you had the CD/Download TurboTax software for 2020, but there's really no good way to do it with TurboTax Online. You would have to create a separate test account and create the returns from scratch, and TurboTax Online shuts down after October 15.
