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.
