You enter it as a vehicle expense when entering self-employment income and expenses.
See this TurboTax support FAQ - https://ttlc.intuit.com/turbotax-support/en-us/help-article/import-export-data-files/enter-self-employment-business-expenses-like-home/L1k6HJY4A_US_en_US?uid=mbb2eq78
There are two ways to track vehicle expenses.
1. Standard mileage rate. You deduct 67 cents per mile for 2024, or 70 cents per mile for 2025. This covers all vehicle expenses -- gas, maintenance, depreciation, repairs, and insurance. The only thing you can add on top of the standard mileage rate is tolls and parking. You need to keep records of business mileage (date, time, mileage, and purpose of your work trips).
2. Actual expense method. You keep track of all your work mileage and all your personal mileage. You keep track of all of your vehicle expenses -- all your gas, all your insurance, all your repairs and maintenance, all your depreciation for wear and tear. Then you deduct a percentage. For example, if 40% of your miles are for Uber, you can deduct 40% of your expenses for the year.
The actual expense method requires that you track all your expenses, you can only deduct your work percent of expense you can prove. It's a lot more work, and for most people, the standard mileage rate will result in a larger deduction. You CAN'T just add gas when you fill up, and say, well I filled up the tank on Monday which was personal, then I filled up the tank Friday night and that was for work. And you can't add gas on top of the standard mileage rate if you want to use it.