Hi @ARODRIGUEZESCOT,
Have you solved your problem?
Do you want to save selected date to your Excel table?
I think you have something misunderstanding with the date format within Excel table.
If you have formatted the column as Date, then the value within always expects date value. Even if it display as numbers, it is Date value when logic works.
In addition, make the entire date column format as the same date format.
To tell you the truth, I always suggest a General column type to save the date because you could use the Text() function to format the date as any format you want to, like "dd mmm yyyy"

Then you just need to modify the Update property as below:
Text(DatePicker1.SelectedDate,"dd mmm yyyy")