@madilyndi assuming you are self employed, and you entered the 30,000 business miles related to your vehicle, then it would reflect as an expense on Schedule C. it further assumes that you had a net profit on Schedule C.
The standard mileage rate for business use for 2020 is 57.5 cents per mile. But you don't "get back" 57.5 cents per mile. The mileage expense is subtracted from your business income.
The business miles that you entered are on Schedule C line 44a. If you entered 30,000 business miles, the business expense would be 30,000 x 0.575 = $17,250. You should see that in your car expenses on Schedule C line 9. If you are in the 22% tax bracket, that would reduce your tax by 22% of $17,250, which is $3,795.
If you are a W-2 employee, the tax deduction for mileage is disallowed for tax years 2018-2025. You can still enter it in Turbotax because some states allow the deduction. But even in the states that do allow it, there are other limitations that reduce the tax benefit, starting with the fact that you have to use itemized deductions instead of the standard deduction.
Your employer can reimburse you tax-free if they choose, you may want to have a discussion with them if you are required to use your own car and pay your own expenses as a condition of employment. In some states, it may be illegal for your employer to require you to use your own car without reimbursing you.
If you are an independent contractor, your mileage is an expense on schedule C that reduces your net income (net income or profit from the business is gross income minus expenses). It is not a direct tax credit, but it reduces your taxable income and therefore reduces the amount of tax you pay.