Assuming the date that you describe has been stored in the cell as a
date, and not just a string of digits you can do the following:
Select the cells that you want to reformat and choose
Format > Cells > Number > Custom, and in the area marked _T_ype
enter dd/mm/yy
If the "dates" are currently stored as strings of digits, do the
following:
Select the column containing the dates and go
Data > Text to Columns >
Choose Fixed Width
Next > Next
Choose Date, and from the drop-down menu pick DMY.
Then do the custom format that I described at top.
