What should be my studying strategy for the CFA level 1 exam in the last month if I don't remember what I've studied?

Not remembering what you studied is totally normal. No matter how hard and how many hours you dedicated to read the curriculum. You will try to remember what that IFRS rule says or what is an interest rate parity and you may not recall it. Some topics you may even say “wait… was this in the materials?”

The last month, assuming you understood partially the curriculum, is the most important part of the preparation.

Why?

Because you'll do mock exams. You will test your knowledge and your stamina through good practice.

You have to get used to the exam format, how questions are asked, time management.

By doing exams you will re-study some topics but with a different (a practice) perspective. Believe me, by doing exercises is the best way to test you and learn.

That's interesting

But it's still sad because I often forget a huge amount of material especially before exams...