Let mods update the author of discussions and posts.
The author edit button is added underneath the title/tag edit button for discussions and under the content edit button for posts.
Users with "Update author" permission must also have the "View user list" permission to be able to search for users.
Use Bazaar or install manually with composer:
composer require clarkwinkelmann/flarum-ext-author-change
composer update clarkwinkelmann/flarum-ext-author-change