All you have to do is select the lines you want and then choose from the action on the line checked at the bottom of the page: “Pause the records (System lock)”
Little tip: to avoid repeating the action on each page, increase the number of elements to display per page in the footer. This will allow you to display all your results on a single page and not repeat the manipulation.
Blocking will be indicated by a padlock at the end of each contact concerned.
When your agents process the files, the blocked contacts will not be offered to them.