Hi @nicmare
Thanks for the question. At the moment, there are no fields which you can use to select comments on a post.
I believe it will be possible to use a multi-select field, and use the following tutorial to customize the available choices.
http://www.advancedcustomfields.com/resources/tutorials/dynamically-populate-a-select-fields-choices/
You will need to find some code to query and return the comment ID’s as the select field’s choices
Cheers
E