You would need to create a select field and dynamically populate the values of the select field from the values in the repeater.
You will also need to add a unique identifier field to every row of the repeater so that if anything else in the row is changed this value can still be used to locate it. https://www.google.com/search?q=acf+repeater+unique+id
You will use this unique field to loop over the repeater an locate the one to show.
This is not the best way to accomplish what you want to do. The best way would be to create a custom post type to hold your Ads and then use a post object field to select them.
