You may have different options available to you depending on your system's configuration. If you do not see the Copy From option, you may have access to the Overwrite With button.
You can save yourself time when completing your timesheet by copying data you’ve entered in one of your existing timesheets. You can choose to copy time, comments, or field values from any of your timesheets, even future ones.
To copy timesheet data:
Most Recently Saved Timesheet refers to the last timesheet you saved, which could be a future timesheet, not your most recent previous timesheet. If you want to copy a different timesheet, click Choose a Period, and enter a date that falls within the timesheet period you want to copy.
Changes you make in the original timesheet will be copied to the destination timesheet as you make them, up until you first edit the destination timesheet.
Your timesheet template may not have the copy option enabled.