how do i go to a 5 in maths to an 8 for my november resits?

i’m currently about to resit higher maths in early november this year. i was unhappy with my gcse results as i was hoping for a 6 but was just one mark off😭 however i now feel very motivated towards getting a grade 7 or above as i would no longer be happy with aiming for my original grade. im just looking for the best way to revise efficiently for this one month that i have. i have a lot of time to study for maths now as ive completed my alevel baseline tests, but i have no idea where to start because i didnt revise for maths in my gcses.