You can do either. Easier option is the better one. If you're able to type faster, then do it in a doc. If writing is your forte (with regards to speed) then write it in your notes.
But... the real benefit isn't in doing these questions again, it's in analysing each question, seeing where exactly you went wrong (i.e., which topic) and going back to and solidifying your concepts in that topic and then building on those foundations to fix up your error and make up for what you lacked before.