You can make estimated tax payments online here: https://www.irs.gov/payments
No forms needed.
Be sure to indicate that you're making an estimated tax payment for tax year 2017.
Note: most employers include bonuses in the year-end W-2 and withhold the appropriate taxes (which is what the IRS wants them to do). You might check with your employer about this before you send in any estimated payments.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.