Announced here:
https://www.nytimes.com/2018/02/27/us/politics/trump-2020-brad-parscale.html
Campaign infrastructure here:
http://www.nydailynews.com/news/politics/trump-picks-digital-guru-2020-campaign-manager-article-1.3844519
He filed the paperwork with the Federal Election Commission to run in 2020 just hours after he was inaugurated.
http://www.nydailynews.com/news/politics/trump-picks-digital-guru-2020-campaign-manager-article-1.3844519
President Trump Names Campaign Manager for Re-Election Bid
http://time.com/5177570/trump-brad-parscale-campaign-manager-2020/
And so Forth....