Cannot Change Date (as integer) to date format

The dates in my Excel data table has been formatted as M/d/yy but Quicksight sees it as an integer and I cannot change the format. Error I get “Known date formats were not detected in this data. Provide a date format to transform this data into a known date format.”
Also entries with a date, Quicksight removes/filters that out of my data set.

QuickSight support the following formats when loading data from a file:

In the Pre-Loading Data editor you can select the right format based on your excel file:

Everything is summarized here: