as a sole trader how do i add my subsistence as i am not an employee?

Hi Maggie,
You can’t claim subsistence or mileage as a Sole Trader, you can claim receipts if they are related to your business. 
They are the main differences between Limited Company & Sole Trader when it comes to expenses. It’s much more tax efficient to be a Limited Company, not to mention safer. 
Hope that helps. 
Pete