Troubleshooting user access in JIRA

Problem: User reports "I can't edit fields on an LCSET ticket."

Ensure you are in the jira-administrators group. (To check, go to your profile which can be accessed via your avatar in the top right corner. On the left you will find a list of all groups you are in.)
Go to the relevant issue if possible. If not, go to a similar issue in the same project.
On the issue view, find the "Admin" dropdown next to the workflow bar. Select "Permission Helper". (See Fig #1.)
Enter the user's name and the relevant permission. For this specific case, "Edit Issues" is the relevant permission. Details of permissions can be found in JIRA's documentation.
The helper screen will show all failing conditions that need to be remedied for the user to gain the permission, usually with a link that will direct you to where the change(s) should be made. For this specific case, the user had to be added to a relevant project role. (See Fig. #2)

Fig #1.

Fig #2.