Good day, rich-pearceexcav.
I've got some information about claiming mileage.
In QuickBooks Self-Employed, you'll only be able to claim the mileage for your vehicle. You can check out on this link for more information: Claiming business mileage the easy way.
To track mileage, you can either do it automatically or manually. The step by step instructions are added in these articles:
Since car expenses and mileage are huge topics, and we're unable to cover everything here. You can visit the HMRC to learn more about Simplified Expenses Checker.
If you have any follow-up questions or other concerns with your QuickBooks Self-Employed account, please let me know in your reply. I'll be around to help you out again. Thanks for reaching out to the Community. Have a great day!