That will depend on how the subscription was started.
If you subscribed through the TikTok app from the Apple App Store, the subscription should appear on your Apple account and can be cancelled from there.
click here ➜ If you want to cancel a subscription from Apple - Apple Support
If you subscribed directly on the website, or through a non-Apple device, then it needs to be cancelled through there.
If it appears on your payment method as coming from Tik-Tok, rather than as "apple.com/bill", then it was a direct subscription with Tiktok and Apple is not involved, so cancelation would be directly with Tiktok.
click here ➜ https://support.tiktok.com/en