This part is more of a formality and final sign off by the conference organizer. Similar to the Short Abstract round, it is a basic Accept / Reject.
Under Reviewing > View / Add Reviewers for the Final Papers round, you can add your final reviewers here.

There may only be a handful of reviewers or only one reviewer. You can assign all the papers in bulk using a quick bulk assignment rule.
View the Results
And just like Short Abstracts, you can view the results from the review like so: https://help.getopenwater.com/en/articles/1379161-view-the-scores-and-results-of-judging