how do I log into my bank account to automatically add expenses to my business

If you are using TurboTax Online - Search for Schedule C and use the jump to link.  Then, 

1. Click on Review next to Self-Employment Income and Expenses
2. Click on the Pencil Icon next to your Line of Work
3. Scroll down to click on Looks Good
4. On the enter your income screen, click on Skip for now
5. On the Next up, claiming your expenses screen, click on Continue
6. Click on Connect my Accounts
7. Follow the on screen instructions

If you have already skipped this option, you will need to delete the Schedule C and re-enter it to get back to the option to connect your accounts.  If you are unable to connect your accounts, you should enter your expenses manually.  

Where do I enter my self-employment business expenses, like supplies and vehicle mileage?