You can submit a new W4 to your employer any time you need to make changes. You can reduce withholding by adding deductions to line 4(b):
[![W4 line 4(b)][1]][1]

To know how much to enter in the Deductions section, use the [IRS Tax Withholding Estimator][2] and follow the instructions.  

In the Income and Withholding step of the estimator you can account for multiple jobs, employment gaps, etc:

[![enter image description here][3]][3]


After going through the estimator they will show results with a projected refund and a slider you can use to adjust how much refund you want to get. Sliding that bar down from what it initially shows will bring up a section on how to adjust your withholdings that will instruct you on how to adjust your W4 and also a link to a partially-filled W4 you can use based on your results.



  [1]: https://i.sstatic.net/9I45r.png
  [2]: https://apps.irs.gov/app/tax-withholding-estimator
  [3]: https://i.sstatic.net/mXbvI.png