You've got to change the data type to datetime. First fecht the date column with this:
T = readtable(filename)
then change it to datetime to any format that you need. like:
T.LocalTime.Format = 'MM/dd/uuuu HH:mm:ss'
you find additional information on the documentation of datetime here: https://de.mathworks.com/help/matlab/ref/datetime.html
