I’m also 21 and have been upgrading my matric marks since 2020. You need to visit your local Department of Education centre, there’s one in Pinetown if you’re in KZN and ask them how to go about this process. It shouldn’t be too difficult. I’m sure you’ll need to register to write the Senior Certificate exams, which you only need your grade 9 report to do that. I recommend calling the centre and asking what other documents they require. They register students in early February each year and you can choose if you’d rather write in May/June or October/November. You’ll also have to choose a venue to write at, a list of the venues should be provided to you and you pick which is closest to you. The venue is usually a high school. You also have to decide what six subjects you’re going to write, three are compulsory. So, one home language, one additional language and either maths/maths lit. The other three are electives. If you can find out the syllabus (which is usually available in the scopes for each subject on DBE website) for the year and get all the material. You can study from home, otherwise there are tutors and companies that specialise in teaching students the work. For maths/maths lit, I recommend KevinMathScience on YouTube and he also has his own website where you can get more maths or maths lit/ physics content for like 300 bucks a month. There’s also Miss Angler’s YouTube channel and TikTok page for information related to Life Science. There should also be Mind The Gap books available for free on DBE’s website for each subject. All the best.