Study study study!
For me listening was the easiest part but reading and grammar was the hardest. I’d recommend going through Genki 1 which basically covers everything you’ll need to know for the N5 test and it makes for a good self study textbook because it clearly explains everything. Do all of the workbook and extra work in the book too!
Also, I know the test isn’t until December but Language isn’t something you can cram for so start studying now. Aim for at minimum 1~2 hours of study 3 days a week, you want to spread out the study sessions so you’re not cramming in a bunch of stuff on one day and forgetting it the next. Do a chapter a week starting now and you’ll be finished the book before the test, then it’s just review and practice for the last week until the test.
This site is good for some reading practice pages, although it hasn’t been updated in over a year now.