The Consumer Protection Law gives you 14 days to return goods of proper quality, and this applies to digital goods too - but with one condition: you shouldn't have accessed the content. Since you've already completed 10% of the course, the platform can refuse on exactly that basis. However, it's worth checking the refund terms on the platform itself - some reputable services offer a guarantee period (a week or two) during which you can get your money back for any reason if the material didn't work out.
If the platform refuses, try contacting tech support directly with the argument that you didn't have a chance to assess the quality of the product. Sellers often meet you halfway with a polite approach, especially if it's been less than a month since purchase. Also check how you paid - if it was by card or e-wallet, you can file a complaint with your bank or payment system; they sometimes side with the buyer in cases of unfair trading practices.
As a last resort, you can file a complaint against the platform or report it to the consumer protection agency, but that's a longer process. Keep in mind: winning a refund is unlikely if you actually opened and watched the content, but it's worth trying - especially if the course was expensive and you bought it recently.