Hi Mona, are you saying you deleted a column in your gradebook?
If so you should know that columns in the gradebook are automatically added when you work from the assignments tab and create assignments and assignment groups. To delete a column you have to delete an assignment from the course. This hold true if you are using the new gradebook as well. You can look at more information on the gradebook here: https://community.canvaslms.com/docs/DOC-10241-4152220009