Auto-fill is a function in excel which provides an easy way to fill-in empty cells with either a repeat value, a series of value or just a cell format eliminating manual typing.
1. Go to “FILE” in Menu Bar (Upper-Left Corner)
2. Select “Options”
3. Select “Advanced”
4. Tick “Enable fill handle and cell drag and drop”
and click “ok” button. Now, Auto-fill option is enabled in your excel sheet.