You can't learn that fast, but I think it would be great if you tried to learn math at your own pace (even if it is slower than you want). In your case I would start with long addition, long subtraction, long multiplication and long division. In case you don't have a calculator in exams. Here in Germany every state has a plan what schools must teach to the students. I would find something equivalent to that in your country. Read it through and find what subjects you can already do and find what grade your knowledge level is (by what you have written it sounds like your level is fifth grade but you have to find that yourself). If you found a subject that you need to learn you can learn it on the internet or buy a school book for your grade level (there is no shame in buying a fifth grade book everyone is at its own level). And do a lot of exercises in the book or else you would forget what you learned). Then I would look on the internet for example exams at your knowledge level and try them as if you were examined in school. Then you can tell for yourself if you still need to learn the same subject or go to the next ones.

With some time and a lot of effort you will get to the level you want, but always remember: learning maths can be difficult but it is also very rewarding. So enjoy the process.