Depending on where you are in the world, you might have a preference as to how the date is formatted. To change the date format, go to Administration > Account Settings > Account Set Up > Date Format.
When importing/uploading date fields on your contacts, we make an educated guess on the format you are using, and convert it to the date format you have selected in the above screenshot.
For example, if you upload a date that is 12-26-2021, we will try to convert this to 2021/12/26 if the setting in the screenshot above is used.
Please note, dates must use a number format. Using months and abbreviations may not convert properly.