Hello there, @Peticus.

Thanks for visiting Community.

Please note that entering mileage is currently unavailable in QuickBooks Simple Start. I'd suggest you upgrade to QBO Essentials for you to have this feature.

After you upgrade to QBO Essentials, you will need to enter a vendor bill until you pay/reimburse, a vendor/supplier, because there is no automated way to track mileage.

To do that, make sure to set up an expense account for mileage:

1. Click the Gear icon at the top and choose Chart of Accounts.
2. Click New on the top-right corner.
3. Follow the new account interview and click Finish once complete.

If you have any other questions, please don't hesitate to reach back out. I'm always here to help.