your "dates" are not dates/values, they are actualy text that looks like a date - you wont be able to format them as anything like they are.

in B7, copied down, use this...
=A7*1

you can then format the results as you want. Also, you can either just hide your original data or copy/paste values from the formula over the original data and delete the formulas

A quick test for text looking like value is =isnumber(cell_ref) FALSE is text