1. Browse to your product editor page, the cancelation flow setting is :
- in the product data tab for simple subscriptions

By default all subscription will have the default survey associated to them.
2. If you want to select a specific survey or not have any survey associated, click on the Cancelation survey dropdown. Select the option you want

3. In case you want a specific survey, select the survey in the new field that appeared.
That’s it your cancelation flow is set up for this subscription product. Don’t forget to save your update.