Hi Moises,
The problem with Custom Fields and our date type is that we don’t know the date format for the current date format. For reading out the value for in the column, we can use some functions to make it work automatically, but for editing and writing it back to the database, we cannot do this. We have to choose a specific format and therefore we chose the same format that ACF uses ‘Ymd’.
When you made the custom field with ACF, Pods or Types, you should be able to tackle this problem by installing the integration add-on for that plugin. But since your custom field is shipped with your theme, I expect that it is not shipped with one of these plugins. In that case, you can fix your problem by setting the date format for your column with one of our filters. You can have a look at the example on this page:
https://www.admincolumns.com/documentation/filter-reference/acp-editing-save_value/
Of course, you’ll have to change the custom field key to the themes date key.