Mixed with excel number and date types

I have data mixed with excel number and and date eg : df = pd.DataFrame({'date': ['2000-01-12', '2015-01-23', '42369', '31342']})

How can i change same date(%Y-%m-%) Format.?

https://stackoverflow.com/questions/65535925/mixed-with-excel-number-and-date-types January 02, 2021 at 12:05PM