How can I clear out registrants from pst meetings on an updated form?

If you are referring to this form: https://www.jotform.com/81583755961166, then in the Form settings, the Autofill option is disabled and the Clear fields option is set to Clear on Submit. This should clear out the registrants. This will ensure that the form will not have prefilled data if that is what you were referring to.

Do review and if this is not what you were looking for, then kindly explain your requirement in detail so that we could guide you in the right direction.