* The manufacturer's website: The manufacturer of your mini chopper will likely have a manual available on their website. This is the most reliable source for a manual, as it will be specific to your model of mini chopper.
* Online retailers: Online retailers that sell mini choppers often have manuals available for download. These manuals may not be as comprehensive as the manufacturer's manual, but they can still be helpful.
* Hardware stores: Hardware stores that sell mini choppers may have manuals available for purchase. These manuals are often generic, but they can still be helpful if you can't find a manual specific to your model of mini chopper.
If you can't find a manual for your 90cc mini chopper, you can also try contacting the manufacturer directly. They may be able to provide you with a manual or at least point you in the right direction.