Suppose you are looking at a worksheet which contains dates which can’t be formatted as “real” dates because of their structure:

Select the date(s), and use Data tab, Text-To-Columns.

which brings up the Text-to-Columns wizard:

Even though the dates are fixed width, in this case you can simply click “Next” twice.

In step 3 of wizard Select Date, YMD:

If you click Finish now, the result will replace the dates. You can select another destination cell:

Here is the result: