Hey! I retook my A-Levels although in my situation I was able to go back to sixth form and sit in the lessons like a normal year 13 student, I don't think that helped very much though. I believe it was all down to my own personal hard work in my resit year that got me the results. My situation was I achieved a grade D in biology and never understood how to revise or prepare for the exam after 2 years. I was always convinced that I understood the content but when it came to the exams, I did badly in every single paper. In my resit year, I continued going to lessons regularly at school but that did not help at all. I had the same teachers who were terrible at teaching, didn't really gain any advice on how to improve as felt like they didn't have hope in me. Not to mention, I actually received 2 years of private tuition (from a student not professional teacher) for biology upon achieving my grade D and was so disappointed I wasted so much money and still came out with a bad grade.
So in my resit year, I quit having private tuition but continued attending them time wasting sixth form lessons which were just a repeat. I believe my mentality of knowing that it is my final chance at this resit got me to work extremely hard on my own to see where I went wrong. I purchased my exam papers that I failed in to understand where I went wrong as I marked it with the mark scheme. I then did so much research and tried to adapt to the exam technique examiners want by trying to understand every mark scheme against exam paper. I was doing all this hard work only to pray that I would achieve a B grade. Miraculously, I exceeded my own expectations and achieved an A grade and that was not because I was able to sit in my sixth form lessons, but down to my own effort!
My advice is just don't be worried about not being capable of retaking the exam on your own! I'm sure if you work really hard, your motivation will guide you towards the grade you desire. I advise that you purchase your past exam papers to try and understand where you have went wrong in the exam.