All Local Authority websites will have a search facility. Enter Subject Access Request into the search field and the relevant page should appear. Some Local Authorities place all the information on a Freedom of Information page, so if a search under Subject Access Request does not give a good result, try searching Freedom of Information and you should find Subject Access Request information on that page. Some websites can be easier to navigate than others, a few are not great, so if you are having difficulty finding the right page then please email connected@careleavers.com for help.
Good luck, to all care leavers out there with trying to gain access to your file.