Do you have a link supporting that appointment info?
Don’t remember where I saw it but here’s one article.
Mississippi GOP Gov. Phil Bryant will select Cochran’s replacement, who will hold the seat until the special election. Senate Majority Leader Mitch McConnell has urged Bryant to appoint himself, according to a person familiar with the discussions.
GOP Sen. Roger Wicker is up for reelection in November. With Cochran’s retirement, a special election will take place the same day to fill out the rest of Cochran’s term, which runs until 2020.
https://www.politico.com/story/2018/03/05/cochran-to-resign-april-1-437126