Only users with access to All Financial Data can export data from Runn. Please check if you have the right permission level if you don't see the Export Tab.
Export for All Projects
You can export the assignments of all projects for a set date range to a CSV file.
Go to your Account Name in the top right corner, click Settings
Click Export in the menu bar
Choose Assignments and Group by Raw
Select a date range
Click Export Data
Export a Project
You cannot use CSV to export data for only a particular project. You can export a full list and search for the project you want from there.