As a JSM administrator and JSM customer you have access and can open Modify My Request dialog on the JSM customer portal.
→ From the a Request view page on Atlassian Help Center you can find Modify My Request button. Clicking on Modify My Request button it appears dialog, that can be edit and saved. From Modify My Request dialog you can edit Summary and Description fields.
JSM Help Center customers can edit:
Summary
Description
