If the student was previously at your school, they may have a profile which is off roll. Go to Admin > Students > Search Not On Roll and search for the student's name. If the student was at the school previously their profile will be found here, and the imported CTF will have merged with this record.
Once you have found and selected their profile, click on 'Reinstate' and this will make their profile live again, with the start date set to that day's date. Amend the entry date on the extended tab if the student returned to the school on a date prior to the CTF being uploaded. If you check the School History area on the Ancillary tab you will see the dates they attended the school previously.
If you cannot find the student profile in the off roll area, you may have incompletely uploaded the CTF. Go to Admin > Students >Full ATF/CTF Importer and try uploading the CTF again. If you do not have an enrol/merge button to click, please upload the CTF in Admin > Secure Upload then email email@example.com, providing the last few digits of the CTF number to enable us to identify it.