Would it possible to redo Year 13 at 19-20 because:Watch
Would it possible to redo Year 13 at 19-20 because you dropped out in Year 12 due to Mental health being really bad etc?
Only a limited number of colleges do A level, but you would start from the beginning.
Your other options are online A levels as a private candidate, self taught as a private candidate or access course.
If there's a particular course you want to do with those a-levels, you could do an access to higher education course, or try a uni foundation course or apprenticeship to get there.