Welcome to the thread, @lahawk81.

If you have an extra withholding that you want to withheld each pay period, you can enter it in line 4(c). This includes any amounts from the Multiple Jobs Worksheet if this applies to you. 

For guidance on how to enter employee's W-4, you can check this article: What’s changing with the Federal W-4?. 

You can also visit this IRS website to know more about the 2020 Form W-4: https://www.irs.gov/newsroom/faqs-on-the-2020-form-w-4.

If you have any other questions, let me know by commenting below. Have a great day!