There is a filter that you can hook into and pre-populate a field. The documentation only shows this for Select fields, but you should be able to use “date-picker” to prepopulate all Date Fields, or you could lock it down to that specific date field if you reference the field key.
https://www.advancedcustomfields.com/resources/acfload_value/
The format of the datepicker is YYYYMMDD
