Each video you have already posted keeps the TAP link (the higher-commission link) it was posted with. For the cancellation steps themselves, see Cancel your Soco subscription.
When a TAP link on a posted video can change
This happens in only two situations, and cancelling Soco is not one of them:
The TAP campaign ends. The brand controls that, not Soco.
TikTok itself removes or updates the product link, for reasons unrelated to Soco.
If you switch your Soco link to a different link
Overriding your Soco link with a different link only affects the videos you post from then on. The videos you already posted keep the link they were posted with.
Next steps
Your next question is probably one of these: