Are you a W-2 employee or are you an independent contractor? If you are a W-2 employee you cannot deduct mileage on a federal return. If you are an independent contractor you can enter the mileage on your Schedule C with your other business expenses.
W-2 employees cannot deduct job-related expenses on a federal return. Job-related expenses were eliminated as a federal deduction for W-2 employees by the tax laws that changed for 2018 and beyond. Your state tax laws might be different in AL, AR, CA, HI, MN, NY or PA.
If you live in a state that lets you deduct job-related expenses, the information will flow from your federal return to the state return, so enter it in Federal>Deductions and Credits>Employment Expenses>Job-Related Expenses