As of now the CSV import feature does not support adding, editing or deleting entries in timesheets using import utility. Alternatively, you can add,edit or delete entries in timesheets by using the Import engine for the version of Web TimeSheet that you are using. You would need to create a csv in the specified format for the #TIMESHEETADD, #TIMESHEETUPD, #TIMESHEETDELCELL commands, this format is defined in the data import utility guide which can be accessed from the link given below.
Provide the csv file to support so that they can import the data for you.
Note: The "#TIMESHEETDELCELL" helps to remove the time and comments entered against a project for a specific date in a timesheet.