Problem
You can't edit the Opportunity and Estimate Follow-Up report to add a campaign column. The report permissions are set to view only instead of view and edit.
Solution
Grant permission to Estimates reports in Enterprise Hub
Go to Enterprise Hub in your ServiceTitan account.
Click User Management.
Click Roles.
Select your administrator role.
Select ServiceTitan permissions.
Find the Reporting section.
Use Ctrl+F to search for the Estimates report.
Select the Can View and Edit permission.

Save the changes.
Go to the Opportunity and Estimate Follow-Up report in ServiceTitan.
Click Edit Report.
Add the Parent Job Campaign column by checking its box.
Click Apply Changes to save the column to the report.
Save Changes if you want to keep any filters for future use.