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):
To know how much to enter in the Deductions section, use the IRS Tax Withholding Estimator.
In the Income and Withholding step of the estimator you can account for part-year jobs:
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 to anything lower than what it initially shows will bring up a section on how to adjust your withholdings.