You can cancel your Free Trial or Tickertape Pro membership anytime you like from the Membership page

Clicking the End Plan button will cancel your free trial/Pro membership and disable the auto-renewal and you won't be charged any further for the plan.

You will still be able to access the Pro features of Tickertape in your account for the remainder period of the plan (if any). Post which you will be switched to the basic version of Tickertape account.