Using the default lemmy-ui you first have to find a post or comment that the user made in your community. Then you should be able to use the pop-up menu for that post/comment to unban them. It may be helpful to go to the user’s profile and search for a relevant post or comment there.
If you are comfortable using the API directly, you can send a POST request using a tool like curl or a browser plugin like RESTED. The site below provides a reference for formatting Lemmy API requests. Set ban=false. It’s a pain, though; you first need to get the community_id, person_id, and your session authentication cookie as inputs.
https://lemmy.readme.io/reference/post_community-ban-user
Yes, voters choose the candidate when they participate in the primary. But before the primary ever happens there’s a lot that goes on in terms of determining who will run in the primary, and what resources they have to run a viable campaign.
https://www.vox.com/policy-and-politics/2017/11/14/16640082/donna-brazile-warren-bernie-sanders-democratic-primary-rigged
Not only did the DNC go out of its way to steer resources toward Clinton, there were leaked emails wherein party officials were brainstorming ways to undermine the Sanders campaign with negative messaging.
https://www.npr.org/sections/thetwo-way/2016/07/23/487179496/leaked-democratic-party-emails-show-members-tried-to-undercut-sanders