Update this excel (download here) with the right info. See in the Excel the second tab: How to (Yellow fields are mandatory)
Note: Make sure your info in the excel is correct! You an not undo the upload!
2. Go to Menu > Attendees and click on Import from Excel
3. Choose your file and click on Upload & import
4. Check if all columns are matched right > match the unmatched columns and click Complete Import
5. Wait until all your attendees are imported :-)
Note: You can check if it went well via Exports > Exports seating List > Download in Excel > scan the excel if it matches your upload.