Rick Famuyiwa, John Francis Daley and Jonathan Goldstein were all at one time attached to The Flash as directors, with many other big director names considered as well. Since then, the hot potato has landed in in the capable hands of Andy Muschietti, who is primarily known for directing horror movies Mama, It, and It Chapter Two.
Article source: https://www.cinemablend.com/news/2548168/the-flash-producer-provides-an-update-on-the-film