How can I unassign a group

-- url of the page with the problem -- : SoAct.org
-- HikaShop version -- : 4.2.2
-- HikaSerial version -- : 3.0.1
-- Joomla version -- : 3.9.13

I wanted to use the subscription to provide membership access based on user groups.
I need to be able to automatically remove a user from the group after their subscription expires.
How can this be done?

Example:
Once a user purchases product "X" for 30-days, if they do not renew, then they should be removed from the user group.
I need the user group to revert to Registered user.

If this can not be done I cannot use the subscription and would like a refund.

Please just cancel the purchase - I love Hikashop but the subscription comp just does not have all the elements I need.