How to claim tax relief on mileage - self assesement

I am an employee. I occasioanally travel for work, driving my own vehicle. My employer provides expenses for the mileage but the amount paid is less than the 45p rate. I have to complete a self-assesement each year. Whereabouts i.e. what section in the online form do I need to add the values for this?

Hi,
On the employment page you need to answer yes to the question, Do you wish to claim any employment expenses or capital allowances while working for? This will then open the expenses section to complete.
Thank you.