To automatically set the end date when the start date is changed you would need to build custom javascript, here is an example: https://www.damiencarbery.com/2020/06/acf-date-picker-set-end-date-to-after-start-date/
To require it to be after the start date you need to use an acf/validate_value filter, there is an example of this here https://support.advancedcustomfields.com/forums/topic/how-to-use-acf-datepicker-for-start-date-less-than-end-date-validation/
