You can change the date & time format in Google Sheets & Excel Online using this guide. Use different date & time formats in spreadsheets.

If numbers keep changing to dates automatically in Excel or if Excel changes dates to random numbers then this post will help you fix the issue.

To change the formatting to display a date in Microsoft Excel, highlight the cells you want to change. Right-click one of them and select "Format Cells." When the Format Cells dialog box opens ...

How to return a sequence of dates in Excel Excel’s fill handle can generate a quick list of dates for you, but the list is static; you must create a new list if your needs change.