As a JSM Help Center customer, you can use Modify My Request on the JSM customer portal for every request you are the Reporter or Creator of.
The button Modify My Request appears in the request below its Summary.
Clicking on Modify My Request button expands a box where you can edit and update the Summary and Description fields of the request.
JSM Help Center customers can edit:
Summary
Description
Portal request can be edited by:
Creator
Reporter
Portal request cannot be edited;
if there is a resolution set for the ticket
if edits are disabled in Jira for this request status